I use 1989 NF5 cylinders and heads on my MC21. Like Stephen said, you can't use RS pistons, but there are lots of others that do work. You will have to make new brackets and adaptors to get the power valve pulleys to work. I dont know how Tyga pipes would perform with RS barrels (Matt????)Other than that, I don't know why more people dont do this. If done properly, it makes a beast out of a relatively gentle 250......and it is still a 250!