If I went for a GT or G40 exhaust manifold on my 2G engine, how would I mate it up with the rest of the exhaust system on a Mk2 saloon? Would I have to have a custom one made up or is there any way I could get a GT or G40 downpipe to attach to the middle/back end of the saloon system? Isn't there a difference in pipe diameter? Any info most welcome.

Just extend the tailpipe

G40 exhaust manifold and entire system, then a longer tailpipe, I'm *sure* that's all VW did.

With a GT system, it will all mate up to your existing manifold.

VAG supply a mk2/3 saloon GT backbox. Probably expensive though.