Jenro, if you're lost in this conversation (I know I would have been when I was new to the SKS), here's a bit of background info for you.
Yugoslavian production of the SKS progressed in a pretty straightforward manner. First came the M59 variant, which for all intents and purposes (minus the non-chromed barrel and different wood types), is virtually identical to your generic Romanian, Chinese, or Russian SKS. These M59s consist of Long Barreled Yugos, B Block, and C Block S/Ns. At the D S/N block, the design was changed to the M59/66 with a permanently attached grenade launcher, grenade sight ladder, rubber recoil pad, and manual gas valve in the gas block. From there Night sights were added and this gives us the M59/66A1 variant.
This is what the front sight block looked like off of a D block M59/66 w/o the night sights:
And then notice the slightly different FSB with the flip up blade when the night sights were used:
Very few D blocks in original M59/66 condition exist. I have not seen E block or beyond guns that do not have the night sights installed.
The original grenade launcher used from block D through block I was a square backed ported design which look like this:
As the years progressed and the design changed, the GL changed to a square backed unported design:
And the final GL change went to an angle backed unported design:
When Justin talks about getting the rifle back into ORIGINAL condition, he means an original D block M59/66. This is quite a bit of work including finding parts that would require a ton of searching. I think most here would say that it's probably not worth it considering what you;re starting with. Now to simply unbubba the gun, get a Yugo stock & hanguard, replacement receiver cover, and a new bayo & components and you should be golden.