May be too much cam for the heads, i know of an identical situation about 3 yrs ago. 598" Brodix 2 extra heads, tunnel ram with 2 1150's almost the same cam, in a 2600 lb Vega. Thr car would not run less than 5.70's in the 1/8 mi, it would run 5.30's with 400 shot of nitrous. Heads were ported but wouldn't flow over 370 cfm. He has since torn it down and going with another combination. Another problem he had was it had 2 1/8" headers with 4" collectors.
These are just my opinion of what was wrong with the Vaga motor and may not be your problems.
Zip.