Frazz,
After you've checked the two linkages to the gearstick and with engine not running, select first gear and jack up one front wheel: can you turn the wheel? (answer should be "no" because the diff/gearbox/clutch and stationary engine should make it at least very difficult). If you can't select the gear, jack up first and get someone to rock the wheel a little while you try to put it in gear.
If "YES", you have a disconnected drive train somewhere. Unlikely to be drive shaft splines if you managed to get the suspension reassembled OK. Could be the clutch friction plate if it's seriously damaged (potentially caused by forcefully bolting the bell housing to the engine while splines were not aligned/engaged.
If "NO" (i.e. drive train apparently connected), we need to know whether the clutch is disengaging. Aside of the noise when depressing clutch, are you able to select first (or any) gear while the engine is running? If "NO" the problem may rest with the release mechanism. For instance, could the release bearing have slipped off the shaft during the transmission refit and the noise be the release fork hitting the spinning tines of the pressure plate?
You might want to check my clutch renewal guide in the "guides" section. There's one for Mk1 and another for Mk2.
red