Help on 408 build

Yes gaskets only is the least expensive "fix"
and a re-builder shim and thick gasket is cheaper than Cometic
and the cometics like certain finish on the heads and block- so check that
IMHO you can't build a decent street open chamber motor Bib block or small block
racing with race gas, keep the revs up- big cam yes or even premium running super stock
tall gears, stock converter, and pump gas no
Do what you have to do
just do it before you break something