Old thread but more info to contribute since I'm late to the party. This is a lot of info from a few books and declassified Top Secret and Secret CIA documents crammed into a summary. Clearly the country of origin for the /1\ SKSs is North Vietnam but this doesn't really answer the question at hand of whether they actually produced the weapon in whole but this does provide a little more insight surrounding this period of time. Long write-up so bear with me.
Background: At the time North Vietnam had a large measure of independence within the Communist Bloc, and it avoided committing itself to either side in the Sino-Soviet dispute. They avoided taking a clear-cut stand in favor of either party and had continually worked to bring the two together. Ho Chi Minh pursued the role of mediator, with at least superficial success, at the 1960 all-party conclave in Moscow, and had persisted in his efforts to heal the breach. Ho’s skill and his prestige a senior Communist statesman, an associate of both Lenin and Stalin, has contributed to North Vietnam’s ability to avoid committing itself when other Bloc parties had done so.
In any event, Moscow, Beijing, and Hanoi almost certainly agreed on the classic principle of combining military and political action, with the differences being a matter of degree and emphasis.
North Vietnam had received extensive economic support from the Sino-Soviet Bloc. The initial phase of the Bloc aid program consisted largely of grants to support the North Vietnamese economy after the partition in 1955. Foodstuffs and other consumer goods were dispatched under these grants as well as equipment and materials for economic reconstruction. The reconstruction effort was merged into a broader buildup of the economy in 1956, which required additional financial aid during the period 1956-1960. A third round of financial assistance was extended to North Vietnam in 1960-1961 to support the economic development anticipated during the First Five-Year Plan (1961-1965). The Sino-Soviet conflict probably had some adverse effect on Bloc coordination of the foreign aid program in North Vietnam, but to what extend is hard to determine.
During this period Communist China was the largest contributor of aid to the development program of North Vietnam.
Ho Chi Minh regarded the Soviet Union and China as Vietnam's big brother and big sister, and he hoped for united Sino-Soviet support for his revolutionary cause in Vietnam. Russian and Chinese leaders agreed to give Hanoi full support. The growth of U.S. military involvement in South Vietnam, culminating in the formal establishment of the U.S. Military Assistance Command in Vietnam (MACV) in February 1962, which caused Russian and Chinese leaders deep concern. In order to meet Hanoi's urgent needs, Moscow and Beijing gave high priority to supplying arms and military equipment to Hanoi.
Before 1965 the Communist forces fighting in South Vietnam were equipped for the most part with old French models, holdovers from the French-Indochina War, as well as captured U.S. equipment. Weapons of Free World origin accounted for almost 60 percent of those captured in South Vietnam. North Vietnam’s inventory of military equipment before 1965 consisted largely of older infantry equipment left by the French and some ground equipment, propeller aircraft, and naval craft supplied by Communist countries during the years 1954-64.
Only limited amounts of Soviet and Chinese weapons were in use at this time.
Military production in North Vietnam was limited to small amounts of infantry weapons, mortars and grenades. Vietnam served primarily as the funnel for the infiltration into South Vietnam of military supplies from other countries.
After mid-1965, Communist military forces in North and South Vietnam were equipped increasingly with a modern family of weapons supplied by Communist countries. Communist China and the USSR were the major donors of military equipment to North Vietnam and to Communist forces in the South, but some infantry weapons, mortars, rockets, and light artillery came from North Korea and the Eastern European countries. Most of the more complex material for the defense of North Vietnam came from the USSR, including heavier field and antiaircraft artillery, the SA-2 missile system, more advanced radar and aircraft, and various types of armored vehicles. China supplied most of the infantry weapons, mortars, and rockets used in South Vietnam.
Small quantities of equipment and weapons from North Vietnam, North Korea, East Germany, Bulgaria, Czechoslovakia, Hungary, and Romania were also used in Vietnam. Most of the weapons observed in the South since 1965 were manufactured since the Korean War. Although the USSR and the Eastern European Communist countries had supplied weapons manufactured primarily in the late 1950’s, most of those were still used extensively in their own armies. Some Chinese observed equipment had reached South Vietnam six months after leaving the factory.
With the initiation of the Rolling Thunder program in 1965 and Hanoi’s increasing direct involvement in the war in the South, both North Vietnamese and Viet Cong regular forces were equipped with modern weapons, including types that were standard equipment within the Communist donor countries. North Vietnam’s defenses were greatly expanded and strengthened by the introduction of MIG-15/17 and supersonic MIG-21 jet fighters and the SA-2 missile system as well as by the addition of light and medium antiaircraft artillery and radar. The USSR was the major contributor to the buildup of North Vietnam’s air defense. Communist China upgraded North Vietnam’s naval capability and provided most of the infantry weapons used by North Vietnamese and Viet Cong forces. The European Communist countries are not known to have supplied appreciable quantities of weapons to North Vietnam or to Communist forces in the South.
North Vietnam had to rely on outside assistance for the vast amount of infantry weapons and ammunition required for its forces in North Vietnam and for the reequipping of the Viet Cong and North Vietnamese forces fighting in South Vietnam.
Only a few light infantry weapons, grenades, and ammunition were manufactured in North Vietnam. Communist China was the major source of infantry weapons, and smaller amounts were supplied by the USSR, the Eastern European countries, and North Korea. Most of the combat material that furnished Communist forces in South Vietnam was infiltrated from North Vietnam through Laos, although small amounts were infiltrated through Cambodia.
Here is another CIA declassified document authored in 1968 (declassified in 1998) that outlines the first observation of weapons in Vietnam. This doesn't include observations after 1968. I only highlighted the 7.62mm carbines observed in country at that time up to 1968. In the case of North Vietnam it was first observed in 1965. Throughout this document the CIA Analyst notes North Vietnam as producing limited amounts of small arms and ammunition, to include the SKS. But again, that doesn't necessarily prove to the level of production.
We do know they produced weapons long after the Vietnam War as the video shows but that doesn't prove the level of production (likely with aid and assistance) during the Vietnam War. Here is a known example of the TUL-1 LMG produced in Vietnam in 1990 as additional info.