I figured it out. The barrel trunnion I used was different than the German 1-piece design. The bullet guides are milled integrally to the trunnion on German guns. The one I used was a US made one that, little did I know, was a 3-piece design. The trunnion is milled first, then the two bullet guides are pressed, then welded in.
So, it sucks to be me, because I welded in the trunnion without any bullet guides in. I think I will still be able to get them in without having to tear out the trunnion, though. It'll just be a ton of fun!
This is the pic I stumbled across that tipped me off: