Afraid unrealistic and not possible my friend.
I beg to differ.
(Left 03-05, Right 06+)
Considering the Grand Am car:
On one hand they've done a lot of weight saving you'd struggle to do on a road car, but on the other hand, they would have also had extra weight from parts that aren't required on a road car. Plus they were restricted by the min allowance, so they could have gone even lighter.
And then there's this guy who managed 2725lbs / 1236.039kg and that's with a roll cage and a few things left to do.
Bit of Google-fu on the potential improvements that guy can do:
-Swap the boot and glass for CF + Lexan and you save 50lbs
-Ti exhaust will save 50lbs
-Lightweight headers and cats is probably another 20lbs
-Replace doors and panels with fibreglass or CF
-Other windows with Lexan
-Cut out some metal bits
Looking at sub 2600lbs / 1180kg.