i've have a FORT cross bike, an older model made from 7005 aluminium, loads of fun to ride and spins along nicely, had a paint job done on it by argos (in my gallery)
also my boss races 2 FORT crossgaurd frames, specced with ritchey bar stem forks and seatpost, the world cup stuff with carbon token cranks and spinergy tillium wheels (cos he's a ponce!) running mostly ultegra gearset in 8speed (clears mud better) it's ti bolted to the max and drilled all over! he does justify it though, he came 1st last year in the wessex vets league and 2nd this year (including 7th overall i think)
so those bikes definately work!
Agreed - Forts are good frames; I've got the Foco steel version (no longer made) and it's built into a really good 'cross machine. As for the original poster's question; retro bikes do have the drawback of less mud clearance than modern ones , speaking from experience - my old 'cross frame was an Edison Columbus SL from 1986 which tended to easily clog up with dead leaves & stuff during races!! By the way, Jonnyboy - I'm about to move down to Hampshire to start a new job (in Winchester to be exact) in a few weeks. Any recommendations for good off-road training locations in that neck of the woods?
 Apparently tyres were smaller back then, so clearances could be a tad tighter; 28mm tubs were the norm rather than the 30mm and 32mm clinchers that seem to be common now.