The difference in 90 spec and pre 90 spec is the side sills and big bumper fitment arches. The difference in 90 spec and G60 arches is 20mm at the front and 10mm at the back, the side sills are the same.
There are some differences in the 90 spec and pre 90 spec body work. Pre 90 have a thicker bumpstrip which runs horizontally along the doors and rear quarter (3dr). They also have an aerial in the wing and not a bee-sting in the roof
The G60 arches look daft on 'normal' wheels, but look awesome on wide rim/stretch tyres - might have to go this route if mine get any fatter!! GPC in Bedford, Euro Car Parts, and VW still do original arches and side sills, just compare the prices and buy buy buy!!
Lewy