I dont know what a j-motor is, any pics?

Hey guys, got a question about J-motors. I hear that a j-motor cylinder will fit a 650/750 block. Is this true?
How can a "large four" top end fit on a small "small four" bottom end?
If someone has pics of these engines please post so I can familerize myself with this engine.

The J motor was put in a Kaw in 1981... just under 1000cc. I doubt the cylinder would work on a 650/750 engine case. While the cylinder studs might fit, look at the stroke of the J motor. It will be different than a 650/750 I suspect. I am not sure how the pistons from a J motor would work on a 650/750 rod and when these pistons came up to the top, a different stroke would mean they would either come up too high or low.

I just happen to have J and 750 cylinder blocks sitting beside me right now, and I can assure you there is no way that a J block will bolt on a 750 bottom end.

The bore spacing is larger on the J, and the stud holes are nowhere close to lining up.

J block is about a 1/4" wider also.