www.MG42.us

The barrel stop tabs are in 3 different places.
from front of BB from rear of receiver
to the back of the stop
Top 18 5/8" 18 15/16"
Bottom 18 11/16" 18 7/8"
Left 18 7/16" 19 1/8"
any ideas on what to use as my #?

I think you are talking about the barrel stop rivet points? The 19.5 dimension is the registration edge of the stop, not the rivets. Are you working with a cut receiver that still has the B stop in it? I couldn't really follow your description.