HP and TQ are about right for the combo as stated imo.
The modest lift on the cam, chevy geometry rockers and lack of port work to work with the larger valves are three stand out reasons I see.
We recently did a 9.75 to 1 466
Budget ported small valve heads 307/180 cfm @ .600" lift
219/227 voodoo cam .540" / .552" lift on a 111 lsa and l07 ICL
Curved distributor with 34 total degrees timing. More did not make more power.
425 hp at 5000 rpm ''UNCORRECTED'' Multiply figures by 1.03 for STP gross HP
515 tq at 3300 rpm
Add rpm intake for 440 HP
This combo consistently makes these numbers on our local dyno which is the tightest one in the puget sound area.
This same combo with 10.3 to 1 static, Budget D3's, same voodoo cam and an rpm intake with 750 DP took a 3900 pound torino cobra to [email protected]
More port work with attention to the intake side !!!
proper roller rockers going to 1.8 ratio if the pistons have large valve reliefs and heads have dual springs.
You would pick up power no doubt.
Hope this helps.