Well. It seems like you don't really want help. But I'm a sucker for punishment. So here it goes.
Yes, the exhaust is all wrong. And YES exhaust contributes A LOT to your power loss.
Congrats. You've put an exhaust on there that can support a whopping 289 horse. What did you say you thought you ran at the track again? Oh right, about 300 horse. Put those headers to work and put on at least a 2-1/2 inch system.
Carb is wayyyy to small. 750 double pumper fits the bill nicely on something like this. Don't use a vacuum secondary on a car that has greater than 230@50 duration cam.
Piston to head clearance. How did you measure that? If your quench is actually .078, I would try and get it down. the .040 area is great.
Once you do all that. Re-tune and re-time. It will need it.
BTW this is the definition of mismatched combo. Hence why it's a dog.
Oh and try to be decent to other people on here that are offering help and such. We are here to help but not when you give us **** attitude in response.