Tapper to roller cam conversion

Heads are basically the item that determines and engines available power capabilities, to make 450 hp you need heads capable of 450 hp at the rpms you'll need to turn for your displacement to get there and work with the general cams cr intake exhaust etc... needed for that level.

A 340 gonna need to turn around 6000-6500 rpm depending how efficient for 450 hp, with heads probably around 250 cfms with a 240 @ 0.050" ish cam etc..