Figures taken from the 1990 VW Specification and Equipment listing:
Golf GTI 8v 3 door: 920kg
Golf GTI 8v 5 door: 940kg
Golf GTI 16v 3door: 960kg
Golf GTI 16v 5door: 980kg
I can't remember how heavy the Mk1's are, although 840kg seems to ring a bell.