Like Don (B3422w5) said, I'd put on the heads you already have. Get whatever headers you need to make em fit. With the current combo, I think a 1 7/8" header would be better, but if 2" is all that will fit, then so be it.
Also get a better intake manifold. Like fast68 said, an M1 or even a Holley SD would be better. I had a similar combo years ago and the Holley SD w/ the 4500 adapter was faster than the 4500 flange Team G.
Honestly I'm surprised your car isn't faster for what it is.