It's been a while, but I seem to remember there being an issue. When we rebuilt the forks on my brothers RD400, his uppers were trashed, but I had a good pair of 350 uppers. IIRC, the 400/350 innards wouldn't cross over. But I don't remember why. We ended up just installing the complete 350 uppers into the 400 lowers.
I guess the moral of the story is: Be aware, it might not be easy, but it wasn't hard to figure out :P
I guess the moral of the story is: Be aware, it might not be easy, but it wasn't hard to figure out :P