There's the option to pull it all apart, which will check everything, nothing like getting to know a car inside out, but you shouldn't need to pull everything off the chassis.
Are the diffs in the right way round? worth a check as they do only go one way (that's if you've not checked them) removing the diffs isn't a huge task not all parts need to come off, antiroll bars etc can stay on as can shock mounts etc if you look at is closely a lot of these can stay screwed together so not a complete strip down.
Use a sharpie or some sort of marker pen to highlight the text on the side of each diff so it can be read easily save you pulling it to pieces for no reason.
Another quick check will be to take out the layshaft, then you can see if it's a front to rear belt problem or layshaft to rear problem, pretty quick to whip it out just undo one of the layshaft bearing mounts 3 x screws and make sure u don't loose the little pins that the spur and pulley locate wit.
The front to rear belt should have some movement in it, if its as tight as a drum then there's a definite issue. The layshaft to rear diff belt will be a little tighter but not rock solid.
If all else fails give the chaps a Schumacher a call, they will be more than helpful and give you some pointers, with most belt driven cars they don't run anywhere as free as shaft driven vehicles, it won't roll forever with or without a motor and pinion in it but should be fairly smooth with a push mine do about 3 or 4 feet. the new MiV2 is the most smooth.
The front to rear belt in my cars have about 5-6mm of movement and the tensioner pulley is really used as a guide rather than putting undue tension on the belt.
Hope it helps, when you get it sorted look to set 2 deg of camber all round 2 degree rear toe and 1 deg front toe, 5mm ride height and away you go!
(others will have many variations on this but its a good starting point)
