1) No paddle shifter, if I want an "auto-matic" (because these paddle shifters 'always' seem to come with a 'no driver required mode') I'll get a lexus not to mention the "feel" "flicking your fingers" to change gears isn't that engerizing. As for a sequential gearbox, sure, make that an option, Quaife makes one:
http://www.quaifeamerica.com/transmissions/rwd/33g.htm
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2) quaife differential - YOU BET!
3) dry sump - ABSOUTELY! (though the comp couple oil pan and pickup are giving me 75+psi at "any angle")
4) lose some pounds - let me refine this, lower UNSPRUNG weight would be very very good, the wheels are TOO heavy as are the rotors/pistons/calipers
5) comp coupe styling - hmm, maybe, but you can't beat the lines of the GTS, love the curves, more curves
6) Rear exhaust - yes, prefer rear exhaust for when I'm not wearing a helmet, nice to not go "deaf" while drving (that is while using a louder than stock exhaust setup)
7) less cabin heat, do something with those cats, move'm back and use less restrictive(less heavy) units, will save weight and not cook the interior (easier to move them back with a rear exhaust...)
8) Motons or other adjustable shock setup
9) You could go crazy with the motor, move away from the pushrod system...update that
Be sure to "keep" the great seats with built-in racebelt hookups (would be nice to add double eyebolts in the floor to handle a 6-point belt, perhaps slots in the seat bottom so the "groin belts" don't have to wrap around the front of the seat)
If you do any "special editions" make it something more than cosmetic, do some performance go-gos (think ACR).
Forget "lambo" doors, they are a pain in the behind when using garage lifts (I have a Lambo, I can't put it "underneath" another car because I have almost no room to open the door much less "crawl out", so the Lambo always goes "on top").
The gauges should be put back "horizontal" across the top of the dash (like the GTS), the vertical SRT10 arrangement is difficult to view while on the track, I have to "quickly" pickup my right arm when I am on a straight and quickly glance to make sure I'm doing ok, this is very distracting.
If you make a special wheel, make an extra run so you have some spares (think smokecoat VCA edition rims), I would think at least 20% over production needs.
Put a better lock on the center console "glovebox", mine pops open on the track when I'm doing high speed turns, the car flexs too much I guess and it pops open, damndest thing!
Keep the Viper as "junk free" as possible, I know more and more federal regs require more and more junk, do your best to work with those.
that's my $.02
-J