A little advice on engine swap in wifey's 550?

Long time reader, first time poster. So heres the deal, spent all spring putting together a little 550 ltd for the ol' lady. (1980) went great rode great. Was a great little scooter. Long story short. She apparently didn't like running dry of oil. so my question is this. What engines will fit? I have searched and searched with varied answers. All of the 550's will work i assume. 650's and 750's no?I have a MINT kz 440 with 2500 miles. (80 as well) crashed. But its belt drive. (Looks like i can convert?) i'm wondering if the rear motor mount is The same width? The fronts arent the same but i could make that work. The pipes may hit the frame... and of course the air box. Maybe go with pods. (Yeah i know. A bitch to jet from what i hear ) idk... any ideas? Maybe someone on here has done this swap? Or even info on the belt drive swap? This thing just ate its last hot dinner last night so i am still a bit flustered over it. Havn't found any good deals on a decent 550 in the area either. Hmmmm... gotta ger her back in the wind asap. Thanks for any input.

AFAIK only the Z400 / Z500 / Z/KZ/GPz550 engines will go straight in. Later GPZ ones as well as the ZR550 Zephyr are rubber mounted and may or may not fit straight in. The 440 can undoubtedly be made to fit, but perhaps it's easier to move parts from the 550 onto the 440 to make it road worthy?