318 head cleaning question

It'll be easier to get the heads back on the engine if you remove the rocker shafts. Follow the FSM for torquing procedures and specs. You can download it here;

MyMopar - Mopar Forums & Information - Service Manuals

You don't need to remove the valves, springs, etc, but you may want to so you can check the mating surfaces and valve stem guide clearances. New valve stem seals are cheap, I'd swap in some new ones in while I was in there.

Since you have the heads off, may as well replace the 45+ year old harmonic damper, timing chain, and swap in a cam. Since you're swapping the cam (and appropriate distributor gear if needed), and get new springs. ;)

If you're doing it in the car, get some advil. Seriously.