Here's what I did,
I found an MPC 76 Formula Promo kit and converted it to a Trans Am. Modelhaus sells the T/A fender vents. Everything else (Spoilers, Flares and shaker) came from an MPC Blackbird.
The hardest part of the conversion was the hood. Starting with the Blackbird hood, I cut two grooves in it with a file to match the '76 headlights. I've done this twice and if you go slow you can make a convincing hood.
This '75 T/A has a modified hood on it
Here is the '76 Before paint:
completed:
I hope this helps!!