Besides concentricity, spline engagement is one of the few things you can't easily tweak or cheat. <img src="/forums/images/graemlins/frown.gif" alt="" /> Pilot engagement is cake, compared to this...

Removing a half-inch from the bell seems like too much -- I'd not want to knock the flanges down to a quarter inch thickness. For reference, my McLeod bell housing is quarter-inch hydro-formed steel and is overkill, but I'd want more aluminum than that, especially since it is cast. I suppose you could build-up the backside of the front flanges with weld, and you could true up the surface just fine as long as you kept the rear face of the bell unmolested. If you do this, I'd pile on the aluminum only after bolting the bell to the back of the block (got a core motor handy?) to minimize heat-induced movement.

A machinist could easily work the front face of the transmission housing, but that's non-trivial disassembly to get to the bare housing, and you'd have to be careful to mill only those areas where the bellhousing attaches and not where the input bearing retainer attaches. Do-able, but not simple.

IMHO, look to the clutch disk itself -- do you have an old clutch disk that you can take apart? The female-splined hub around which the friction plate is built is generally connected in front of the disk...

Alignment between the flywheel and pressure plate prevents you from just flipping it and running it backward, but a custom clutch house should be able to reman your existing friction plate with the hub behind the plate, and perhaps even a spacer... hard to say what's involved without taking you clutch disk apart. Finding a shop that will do this won't be particularly easy, but I am certain that they exist, as you can get just about ANYTHING rebuilt that has friction material on it, and many industrial applications are one-off deals, where you take them in the old one and they rebuild it. Hit the yellow pages for the closest major metropolitan area -- this a dirt-under-the-nails industry that isn't likely to have much of an internet presence... a clutch CHANGE shop won't be able to do this (they just order parts, and do no rebuilds), but they might be able to refer you to a vendor who can.

IMHO, first see if you can find a friction vendor to set you up -- changing that piece should be cheaper than machining two sides of the bell plus possible the transmission, and it should have least impact on potentially creating intereference inside the bellhousing. If you can't make that work, build up the thickness of the front flanges of your bellhousing, and you'll only need to do one setup at the machinist to scalp the front face where it meets the tranny. Tweaking fron and back of the bell AND front of the tranny is gonna be three distinct setups, which will cost you enough that shortening and cutting custom splines into a longer input shaft may begin to make sense...

Thinking on this sort of stuff is MUCH more fun than cleaning my shop!

Randii