RE: Replacing an engine
Size: .12-.18 is a small block, .21-.32 is a big block.
Crank: Standard or SG. Standard is just threaded and uses a nut with a shaft. SG has a smooth shaft combined with the threaded crank.
Carb: Rotary or slide. Rotary means that a part on the carb rotates to open the throttle up. Slide means there a part pulls out the side of the carb to open the throttle.
Exhaust: Side or rear.