Indeed this site was pretty busy in those days, henceforth the kits have dried up, at least with barrels (thanks to the dingbats in Washington DC, BOTH parties with the 2005 import barrel ban), and with importers mostly choosing to have the receiver rears be left behind in the trade zone facilities on most the yugo M53 kits that are still trickling in, the last man standing is Brian at BRP, a true gentlemen.
My advice, first, you obviously know to do the semi mods before even tack-welding; secondly, I cleaned the slag from my rails and checked the bolt's travel on the rear pieces, it was not uncommon for these pieces to cave a wee bit in on the sides. These receivers were torched, dropped, either bagged or wired together, and piled on pallets, sometimes there were squeezed some, no biggie to expand and fairly easy when still in pieces. Then of course those rail sections get removed anyway, also warping is not hard to do unless you are pretty good at tigging, hopefully you are adroit, if not, there is no shame there just get some MG3 scraps from RTG gun parts and practice, you will be glad you did.
Keep us in the loop, and congrats on finally breaking ground, and unless you are a real wizard and can do your own, I cannot endorse Brian's (BRP's) semi gripstick and semi-bolt set up enough.
“… corporations have been enthroned, and an era of corruption in high places will follow, … until all wealth is aggregated in a few hands and the Republic is destroyed.”
- Abraham Lincoln (Republican), Nov. 21, 1864