Re: rear window
A combination of engine/gearbox lowering, shortening the velocity /intakes pipes of the rear 2 webers, and using a glass window (in my case) instead of 'anything' plastic.
I reached what I think was the limit of lowering the complete unit and my reasoning for that would be a sump protruding below the car and drive shaft angles (which seem to be currently almost neutral). Any further lowering may need a dry sump or a specially cast manifold (the latter being a horrendous cost option) I removed the spacers under the webers (which resemble paxolin but I don't know what they are made of- is it Phenolic, or is that an instrument in the brass section - I don't have a clue). The lowering involved some cross member mods and a the rear cross member above the gearbox (which also has the rear anti roll bar mounts) was remade as well. While it was in the early stage I covered the forward and side engine bay in 18g tp4 as I'd heard some reports of 'forward moving' fumes (especially in the gear change area) coming into various cars. In fact the first GTD I was a passenger in, while some oaf called Simon tried to scare me down in in Poole (GB) was a fume trap. He said that all sports cars were like that. I think he was nicknamed Simple Simon but I cant remember his other name.
I guess that lowering will also help a little on handling but I've nothing to guage it by as I've never driven a 'cooking' GTD. (is there one?)
These mods have all been done on mine and I can try and get you some pictures if you so desire.