RE: MVVS Twins
Bob,
Both twins use the .61 engine's stroke of 24 mm.
The 1.20 uses the original .61's bore diameter of 23 mm and the 1.44 uses the .77's 25 mm bore...
Carefully remove one of the cylinder heads (take care that you don't rotate the sleeve out of line with the bypass and the exhaust ports) and just measure the diameter of the sleeve/piston.