Xtra 10 will fit but you'll have to relocate front and rear mounting plates. Use donor machine to determine locations for the swap. JB Shocks has some of the measurements but I used an Xtra 10 that did not correspond to the dimensions that they show and had to re-drill and remount plates...
sounds as if your float needle is sticking open and not shutting off the fuel. Disassemble and clean thoroughly. Drain fuel from carbs before summer storage to prevent future problems.
92 was the first EFI model. 89 seemed to make the most power. Had a 90 and 91 model and had no problems with them. Picked up a 91 and a 89 this summer for the grandkids. Have finished a complete redo on the 91 and just starting on 89. Good reliable machines. Don't really like the body...