>>63981187
>>63990422 (Me)
>M70B1 had the 1.5mm receiver (same as OPAP) for grenade launching.
And the GL gas block for a B1. Receiver size isn't relevant to the B3 designation.
You're still missing a bayo lug, but the OPAP would be the M70B3N.
That's an opinion since it's not an official designation anyway. But it is based off of the list of the designations and extrapolating the -N from the Yugos with a side rail, as most of the basic M70 variants didn't have an optic mount.
>I could be wrong though its hard to find a good source on receiver thickness
I'm not even sure there is a source for that beyond what people online measure them at, as it's not in any specs except maybe blueprints; as far as I know.
I could also be wrong, though.
>Apparently all bulged trunnion Yugos are 1.5mm receivers, from what I could find.