After finding this:
http://www.luks.dk/pdf/65cc/Manual_65_cc.pdf.pdf
I am sold. The motors in the TXT 70 and 80 along with
the SM and Rookie 50 are Morini M65-C lower gear cases
with different top ends. They may also have different
stroke lengths in the crankshaft.
The LEM RX65 appears to share the same bottom end with
the GasGas as well.

Looking at the 2010 MC65 GasGas, that motor seems to be
something altogether different. So my confusion continues.
Jeff