Yep the later550 uses the same bearings as some of the usd forks but as you sayits stem length that differs.i have no idea why stem swaps are risky. When its all bolted up where can it go as the forks will hold it together, we have done loads eithou problems.Ive got some spare gs500 front ends as ive put a 750srad one in my gs500 with gt500 engine.