[pirati]

I was planning to buy a new fork (Reba 100mm) to build up the 2001 SL frame I bought, but am wondering if I just can't transplant the MX Comp 85mm that I have on my Trek ?

Main question: Reba 100mm is 473mm axle-crown, where MX is 458mm. Will the 15mm difference make a great change to my frame geometry ?

Originally, the 2001 SL had a 80mm RS Duke Race.

 

[Entrenador]

should ride fine in xc settings

Hey, your SL will ride like an XC bike -- climb well, nimble handling, etc. You will lose a bit of the DH stablility that you would have with a 100mm or larger fork, but you could get used to it. make sure you have enough steer tube to make it work.
jc