I'm with Joe on the flat tops, a lot of the AFR heads perform better with flat tops than big domes, something to do with the combustion design of the heads. I know the 388" i built a couple yrs ago did, with AFR 220's angle milled to 58 cc's, it ran 6.30 in a 3,000 lb camero with a toilet bowl on alcohol.
JMO
Zip.