Build a 421, use 5.7 rods and IGNORE what anyone says about rod ratio. This will give you a more stable piston/pin height. My brother runs one with 867 RR Pontiac heads, not as good as your AFR's, has run 5.61 1/8 (not run yet in the 1/4 but about 8.80's) in a 1900 lb SG Corvette roadster. With a 5000 stall, limit the intake duration to around
[email protected], should still run low 9's in the 1/4.