I ran into the same problem recently when converting 2 Saiga's. The holes in the internal adapter on both guns were about 1/16" offset from where they needed to be. I carefully (as careful as you can be with an angle grinder) removed material from the receiver to ensure a good fit with the adapter. On one of the Saiga's the adatper also interfered with the stepped area just forward of the tang and which requred some additional metal bashing.
After a couple of hours of effort I was able to get everything to line-up like it came that way from the factory.
