not quite as easy as that I'm afraid, the handbrake lever mech is completly different.
early cable - 1800mm
late cable - 1625mm
Most of the extra length is down to the fact on the early hbrake the cable attachment is at the front of the lever, and on the late its much further back.
edit: ive heard on the early car you can mount the calipers upside down, only issue with that is to bleed em you have to take em off the carriers and hang them the right way up so the bleed nipples work.
edit2: and yeah the early mk3 calipers are same as late mk2, but its only like the 1st year or so so they arnt so common. Check for a massive spring on the outside, if there is one = mk2, if not = mk3.
Also if you use MK4 calipers make sure you paint them as the alloy corrodes just as badly as the iron. also you get the problem of metal corrosion between the bleed nipple and caliper so they can sieze in! (theres a word for it but it escapes me, corrosion caused when 2 metal types are in contact)
