Sundance, I would not be able to sleep at night
if I were to turn the threads off a perfectly good Russian barrel. My type III is threaded into it's Firingline receiver, and I wouldn't have it any other way.
B-slap, for me pressed barrels are a piece of cake, done plenty of AKM and AK-74 stuff with no major headaches. The Firingline receiver
was a pain for many reasons, even though I had worked on lots of FALs before. I got one of Mike's first 6 receivers, and altough I had fun, it was a learning experience. The basic prob with the thread timing, is that he started it about 180 deg out from where the general ComBloc average starts. You might get a barrel close (like your Polish barrel) or you might be a ways off like some Hungarian and Russian barrels I have seen. 3 years ago when I did my Type III, I started by making a washer to time it, but then realizing you could drive a truck through the headspace gap!
Then I ended up taking down the shoulder as you did, to give me the 15 deg pre load I wanted. In this manner, the lugs on my bolt had to be taken down to headspace the rifle.
No big deal. The real problem lies in the fact that the Russian manufacturing process threaded receivers and barrels roughly at the same starting point every time, and any discrepancies or compound errors were fixed by picking the right sized bolt out of the bins, or custom grinding the lugs to headspace the weapon. You see, the barrels were screwed in bare and blank, tightend, and then the breachface cut was made with a vertical end mill (which BTW guys you will be able to see evidence of this on the inside right of the front receiver stubs when you get them!), the gas port drilled, pin cuts, and barrel parts were installed later. So you can kinda see how it is difficult for Mike at Firingline to determine a good staring point for his threads.
We are kinda 'reverse' building these things here, since your ports, cuts and barrel parts
are already indexed to the original thread timing on your barrel/receiver combo!
For me the AKM/74 style pressed barrel offers TONS of flexibility in headspacing/ R/L alignment, and is a piece of cake.....but what fun is that!?!?
Hope this helps you out-
-C