YZ465H has 43mm tubes. If they're 38mm then they're from something else.
For the most part, any Yamaha dirt bike 38mm forks can be considered interchangeable with other Yamaha 38mm dirt bike forks.
Same goes for the 43mm forks, although the later ones have a horizontal brake lug which may not be strictly legal for Evo at National level (although nobody has been hassled for it yet).
The XT frame runs loose balls for the steering head. All of the 38 & 43mm front ends run tapered needle rollers. You need to convert the 38+ triples to loose balls, or convert the bike to tapered rollers with an aftermarket kit (definitely the better option).
I started a similar project a few years ago - never finished it, for a variety of reasons (mostly not wanting to spend the money required). I know of another one that's been in the build for two or three years now...
With the power of hindsight, I'd go one of three ways:
1. Leave it alone. Get it into reasonable mechanical condition, go ride it, and have fun;
2. Buy a YZ250/465G/H roller to put the XT motor into. Carb clearance/airbox alignment is a likely problem, and obviously the frame will need to be modded, but it will still give you a much better race bike than a modded XT.
3. Buy a Husky 510 or maybe even one of those rotten HL500 things.
If you want a small/lighter bike, then buy an early XR200 (seriously).
Everything else is piddling money up the wall, one way or another.
The best advice I can give you, was learned the hard way:
Just get a safe, legal bike and go race it.
Don't get caught up in the process of building a shit-hot bike to begin with - it won't make a difference to where you finish at first, and just delays your development as a rider.
Personally, I bought a decent DT250 in 1990. I wasted sixteen years f&@king around with it, until I just went and bought a running YZ125D and finally entered a VMX race... I should have just gone and raced the bloody thing... I sold the DT last year, still unfinished, still never raced... *face palm*
