i did the pump transplant to my 550, you have to get a 650 donor hull, cut the bottom out, cut the 550 bottom out, and fiberglass it into ur 550 hull basically, theres alot more work invloved, and its a huge pain dealing with all the foam both cuting the cavitys out and getting some foam back in, totally worth it in the end, but i had a 750 big pin in my 550 with a bunch of engine mods, so it had to be done, the 550 pump couldnt handle it. dont bother switching to the 650 pump with your stock 550 motor, if your talking about freestyle trim, then your sh**t out of luck for a 550. but if you want trim because the ski is porpoising, then just get a scoop grate to keep it glued to the water, extended ride plate, and put shims under the ride plate bolts