to sum up, the whole thing about sachs engines
504- no pedals in the case
505- pedals in the case
A/B head tapered, small ports
C/D head square, large ports. D acutally has slightly larger side transfer ports than C
A and B engines come with 2 2mm rings and very long skirts with small transfer port windows. Most widly available replacement piston.
Upper ring is 1.5 mm bottom ring is 2mm. Not available for replacement. intake skirt is shorter than exhaust, and transfer port windows larger
Upper ring is 1.5 mm bottom is 2mm (not available) Intake and exhaust skirts
D designation on 505's mean the engine has a longer crank stroke length. The connecting rods are the same length.
The Crankshafts between D and the others are the same size.
the spacing between the shaft and te connecting rod shaft are bigger- I'd measure, but it's in m runner right now.
Jafar- make some port maps of what you have. It'll be a good reference!