Carb change to 4 barrel
All depends how involved you want to get into it.
Swapping out the intake manifold and all.
There is a simple Mr Gasket 2 to 4 bbl adapter that works quite well you can use on your existing 2 bbl manifold.
Otherwise got to roll up your sleeves and get deeper into it.
Edelbrock 1406 Electric Choke carbs work good with the Stock 318s. You will need the edelbrock mopar linkage arm to work with it. Also have to reposition and readjust your automatic kickdown linkage so it lines up and works proper with the trans.