Barrel is trivial but would be expensive. You'd likely have to start with a 6.5 blank, and get a lathe or be prepared to pony-up hundreds for a gunsmith to get the AKM contour machined out.
The hard part would be getting the bolt timing right...most AR bolts AFAIK use a more dedicated bolt for 6.5G since its base diameter is a bit smaller. I'm not sure if in troubleshooting you'd simply end up with more rightward ejection patterns, who knows. Extractor spring might have to be tuned if using an unmodified AKM bolt, would be my guess.
Good luck with the build!