No north american quad headlights, but they are produced in Brazil where the fox is known as the 'Voyage'. Thanks to the exhange rate the kits are cheap too.
The '90 fox is the year they swapped to CIS-E injection i believe. First of all, make sure you have replace the exhaust restricting piece! If you go to a VW dealership you can order the gasket which sits between the cat converter and the exhaust flange - the old version was a huge restriction on the engine, the new part number is an Audi piece which doesn't restrict the gases. Performance mods include dual-exhaust pipe from a Dasher etc. An Audi 80 8v pipe may also work with modification i believe. Cams are easy to do and apparently work well. You could drill the air-box on CIS-E to, erm, make it sound better... Get brakes from a 16v GTi etc - then you can stop faster at least. A2 suspension fits the rears, get custom springs for the front or build your own ground control kit.
I forget the link, but search for just about the only Fox website out there, ran by a canadian with a nice white 2door fox. It's got some great tips and facts about the foxes & is a fantastic place to start.