================================================== Andy the reason you don't see Jet Ski Engines being used, is there is many Good Used Rotax UL Engines Available, 277UL, 377UL, 447UL, 503UL, 532UL, 582UL, 618UL, and Rotax Rick offers the 670, all fairly Cheap, and also their Counterpart Snowmobile Engines even cheaper. You also have many of the Kawasaki 340/440's that were popular also cheap. Can you adapt a Jet Ski Engine, Yes. Can all Jet Ski Engines be used, probably not. I don't know about all Jet Ski Engines but the Kawasaki 440/550 used a Threaded PTO. They have a Big Boss around PTO just as some Kawasaki 340/440 Snowmobile Engine had, but not All. The Sled version used an Adapter Plate 3/4" Thick with a Rotax A Gear Drive. Never seen a B Drive Conversion on a Kawasaki. I have seen a Provision 8 Adapter Plate for the C & E Drive. Most Jet Ski Engines don't have Water Pumps, so would have to figure out a Solution for that. Will Fan Cooled/Free Air 440 Cylinders work on a 440 Jet Ski Case, maybe? You could run a Non-Provision Belt Drive like this, Small Pulley could be Threaded for PTO. The Arctic Cat Suzuki 340/440 were copies of the Kawasaki 340/440, so they are a good option.