Forged wheels may offer a reduction. But GM has some pretty severe wheel requirements. I know shopping for my Sky I can find some "race" wheels that save about 8 pounds per wheel. But race means no potholes.
Manual seats for sure, but only a few pounds. I know my Sky has power height on the driver side, but manual for all others. So that can work.
I will let Pedders comment on this. My first instinct is they actually weigh a bit more. But that is a factless observation.
Factless no more we save about 18 pounds with Xa coilovers and breakeven with the Supercars.
I haven't seen the EPS mass. ZL1 has EPS, SS doesn't so if it weighs less it's good. Plus better FE.
LS7 is for sure more power and awesomeness. But just big bucks due to the manual build in Wixom.
I'd hope for a nice LS3 bump. Problem there is you now make the LS7 obsolete. Why pay big bucks for 505 when you can get 450+ for much less.
Gearing something that I think could add an immediate benefit. Honestly not sure why we haven't tapped into this.
I like your numbers, which would require the LS7.
I think your cost is ok, but not with the LS7 which is the contradiction.
But for me, here is what I would do to drop the weight and still have a car pleasant to drive every day.
Start with a 1SS
Eliminate all engine covers and plastic in the engine compartment. If it isn't moving fuel or coolant..............gone.
Manual seats.
No fog lamps. No LS filler. Just a simple fascia.
No mail slot.
No floor mats. (optional on 1SS anyway??)
No trunk trim, no flat load floor, no spare, no inflator. Just a can of fix a flat.
No folding rear seat. Yes, I want a rear seat or I'd just buy a Corvette. But I don't need latches and pull strap to fold it down on very rare occasions.
I'd remove some but not all NVH treatments. Lighter dash mat, reduced mastic materials on the body.
Eliminate the push/push fuel door and add the finger cup back in. This eliminates the push pin mechanism.
Smaller bare bones console. Simple arm rest in between the seats.
No power passenger side rear view mirror.
Go to a 15 gallon fuel tank. Saves full tank of fuel mass and also just a smaller, lighter tank.
Thinner glass for windshield, doors, back light and quarter glass.
That might, and I'm guessing save 50 pounds, not counting the reduction of 3 gallons of gas (an extra 20 pounds)
Adds:
Carbon fiber hood
Titanium exhaust (C5 Z06)
Glass Matt battery (bad for performance, but good for mass)
Magnesium front cradle (C6 Z06)
Low mass race wheels (C5 had titanium but wouldn't go quite that far)
Again, guessing a bit, you might save another 100 pounds.
So total reduced weight 150 pounds over a 1SS.
If at all possible, get the Wixom LS3 (reported to make more power) and add tweak it where possible. Only asking for 450 at the crank.
Now add the suspension improvements from the ZL1 minus MR shocks.
Widen the front tires to help understeer.
Now you have a slightly lighter, slightly more powerful and slightly better handling car.
That will likely not get your 0 - 60 in 4.0 seconds or 12 second 1/4, but might make the rest of your numbers.