Yeah the M70 and M77 both use the "RPK" trunnion with receiver bulges. The M70 is indeed a little heavier of a barrel.

IMHO the Yugos----or Serbs to be correct----might just be turning out the best new-production AK's on the market, if not in the top three. The fit, finish, and quality are there as well as CHF chrome lined barrels. To me the chrome lining is the biggest improvement over otherwise well-made Yugo AK's of years past.