Ok, you need compression!!!
First off I'd get the heads milled, with OEM pistons them big chambered 6x heads will have your compression pretty low > 7.6 to 1 , W/ .050 milling it would bring the number closer to 8.2 -1
My lawn mower has more than that. :shock:
Assuming your doing a complete rebuild, have the block bored/sqaured, and opt for flat tops pistons over OEM replacement slugs.
A competiton valve job (3 angle)
Comp Cams XE274H or XE262H would be good cam choices
Edlebrock performer rpm/ or performer RPM air gap intake
750 CFM holley Dp or equivelant carb
Headers > W/free flowing muffs & exhaust
373's gear in the rear & 2500 converter
Goodluck, Cp