Its a small world. My brother went to NADC and my nephew-in-law is going there now.
Finally at a place I can post some links.
For exhaust options, the best choice for Mk1 cars is at
Mk1 VW Performance Exhaust Systems 1982 should have the dual outlet cast manifold so the twin downpipe that attaches to that (hope your studs are not rusted solid) and the 2" stainless pickup system would be great if cost is not a concern. I've ran the aluminized in TN and it will last here. Not sure how it will last where you are. Aluminized is cheaper than the stainless, it performs the same but wont last the same years as SS.
I had a feeling you would have the FF. There are supposedly some diesels running around with a 4.25 final drive instead of the stated 3.89 final ratio. Not sure if myth or fact. You already have one of the tallest geared transmissions. Only thing taller is one with a 3.67 or 3.65 final.
Lots of transmission info at
Gear Up!
and
020 GEAR RATIOS The gear charts can help with engine RPM, tire size, and speed estimates. There is an excel spreadsheet on the bottom of the scirocco.org/gears page that you can mix and match all kinds of ways. I still think your best bet with the trans is just change the fluid, make sure your CV's are all in good shape and work on efficiency elsewhere.