i just got my set of vauxhall calipers and they really do fit perfectly!! (i was a little worried!!) mine are ATE calipers from a 16v cavalier. they fit with standard mk2 16v discs (256mm) and cavalier brake pads. to mount the calipers you need shoulder bolts as the holes in the vaux calipers are larger than the 8mm ones on the mk1 hubs. i think these are m8x10x25. any bolt supplier will know what you mean!!
i know the only other thing is to sort out the flexi pipes as they are a banjo fitting on the vaux calipers. i've read its not a real issue tho!!
one thing to note is that often, due to the casting process of the mk1 hubs, one side caliper needs to spaced with a flat washer to pull it central to the disc!!
theres loads to read about it posted around!! hope this helps