I've got a new gearbox for my beloved, but it's a 24 spline job, code ATH. I'd like to use it because it has far better ratios for my style of driving, which is smooth low rev/high gear sensible town driving

, with occasional long distance motorway thrashing in the small hours

As far as I know, my current original clutch will take a 21 spline shaft, though I've yet to rip out the current box. I'll do that when me mate is over. It's likely that the clutch is on it's way out, and I don't like it much anyway, so....
What clutches are recommended for fitting on a MK2 8v 1.8GTi? I'm not a racer, I just want a good everyday clutch that's nice and smooth, and will take the new gearbox I've got. Any suggestions? Oh and there's been talk of flanges involved in changing it.... What are they?