Disappointing ET's with 408

Wow. throw that 600 cfm carb as far as you can. you need AT LEAST a 750 if not 800-850. Get a saw and remove the tailpipes. Just put turndowns after the mufflers. Timing seems to be coming in very slowly. I'd like to see full advance by 2000 rpm. How bad are the headers banged up? I'd like to see at least 1 3/4" pipes if not 1 7/8" if you can find them. What are you doing for fuel delivery? At the very least 3/8" line front to back with 3/8" pickup in tank. good electric pump Holley blue will work nicely.
This thing should be a screamer. It should be making at least 550 hp. and you should be running mid to low 11's. what miles per hour are you running?