I know there is someone around here with a huge cowl induction hood made of fibreglass I think, was custom I assume.
(at least on my 96' 3.5L)
The exhaust is kind of wierd I think from the headers to the pre-cats is 2.5" or 3" pipe and after the pre-cats to the main cat which is a 2x 2" inlet and 1x 2.5" outlet which goes to a pretty large muffler around the middle of the car and that goes back to the resonator.
A common mod is just to remove the muffler, with just the resonator it is pretty loud and kind of raspy.
What I did and quite a few others is remove the main muffler and resonator (which is at the rear where the tailpipe is) and just put whatever muffler or glasspack etc.. you want in place of the resonator.
The only person I can remember doing dual exhaust lost some ground clearance which you might not want, because there is no tunnel for the piping on the right side exhaust if you go dual.
I think someone (hybridman?) is working on some 3.5 headers not sure what year, if the year matters besides 1st and 2nd gen.
My next change to exhaust is if those headers work out like he plans and starts selling them, i'll get some of those and run true dual with an H pipe and 2 high flow cats in place of the pre-cats keeping the O2 sensors. That should clear the way for any super/turbocharging in the future.