1978 318

Real world experience with a 318, also in a 78 Power Wagon.
I would just put a new timing chain in it, the original will be shot.
Add 4bbl and intake.
Cheap headers fit fine on these trucks, do use the mini starter.
For the header installation, on hooker headers, throw the instructions away.
Remove the starter, push the drivers header up from the bottom, with the truck sitting on car ramps.
Passenger side, remove the oil filter and drop in from the top bolt them on, no dents required.
Add a good duel exhaust.
That is going to give you the best bang for buck on a 318, and it still will be lazy, but parts can be used on another engine, that is as much money I would spend on it.