Congrats on finishing both days, that's an accomplishment! We run an 86.5 in Chumpcar races here in Texas, and we're dumb enough that we're gearing up for a 37 hour race at Eagles Canyon raceway in a few weeks.
In terms of weight reduction, go for the low hanging fruit. You don't need a dashboard in a race car, you can pull that and secure your gauge cluster by some other means. We're using a simple tach from ebay that has coolant temp, oil temp and oil pressure gauges built in. You can also remove the crash beams from the doors, all of the bracing from the underside of the hood, sound deadening is amazingly heavy on these cars (lots of dry ice in grocery bags is the miracle here, lay it over the sound deadening material to freeze it, then break it up with a mallet and it should fall right off, I think we removed 50 pounds of the stuff). There's also probably 30-40 pounds of useless wiring once you simplify a car for track duty, so you can carefully glean out all the unused circuits if you have some time to spare. We also took the time replace the factory front crash beam with a single piece of rollcage tubing. It's better than nothing and retains a good amount of strength while shedding some weight off the nose.
The Mk3 does get light in the rear once you pull things out like glass, spare tire, tools, etc. We're using ebay coilover sleeves with unknown spring rates and found the car to be too tail happy, so I simply removed one endlink on the rear to disable the rear swaybar, now the car is extremely well behaved on track.
It also appears that you aren't taking full advantage of the tire rules. Our car was an absolute widowmaker until we put GOOD tires on it. Brakes would lock up and were impossible to modulate, the car would spin with virtually no warning, etc. We stepped up to 245/45/17 Falken RT615 tires and the car instantly became brilliant. Do not underestimate the effect of good tires. Buy some inexpensive 17x9 inch wheels and run a 245 tire at minimum. We just switched to 17x9.75 XXR wheels (fairly light at 21.5 pounds, sturdy and inexpensive) and 255/40/17 Hankook Ventus RS-3 tires. I'd like to run 275 width tires all around, but the cost difference for tires was too much for my teammates to get on board with.
