Great photo spread!
Looks like a nice one! The stock is in good shape w/o cracks at the front of the receiver where the rivets stressed the thin wooden section near the crossbolt. That's always a plus on these.
I don't know about 500 number imported (I think a bit higher, they are not über rare like you see with Soviet-Sinos or thin Chinese laminate stocked /26\s), but they are uncommon for sure as you only see 10-20 up for sale per year.
Based on the S/N's in the database, we can say there were at least 5.3k made at [0138] in '70, 6.9k in '71, and 3.6k in '72. There was also a smattering (possibly 1500) made in '70 at [0145], though I only have a single specimen in the database from there.