Help on 408 build

Well I think he has a number of choices and he will have to pick one and take his chances....

Install some really thick head gaskets/shims and maybe push rods cost $500-600. Add another $600 for a cam swap. ( the 1/2 *** fix)

Install pistons that get you down to the mid 9’s SC say $700 for pistons $100 for gaskets and $350 if you need to balance. You can probably get back $350-400 for the old pistons or keep them for a future build. Add $600 for a cam swap ( the 3/4 *** fix)

Keep the bottom end and purchase aluminum heads, you may still need a cam swap even with a 65cc head. Say $2000 for heads, $600 for a cam plus odds end ends probably $3000.
You could probably sell those ported J heads you have for $200-300 if you keep the adjustable rockers. ( the complete *** fix)

Leave it alone and burn race gas ( the no *** fix )

You might consider putting it on the dyno if you really want to tune it...around $500