A little advice on engine swap in my 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.