1974 318 duster. Can I port/polish these heads and get enough power out of them?

Short answer. Unless you have set of templates and experience with a die grinder, proper cutters and a flow bench, more cylinder heads have been ruined than any other engine part.
Buy/borrow as many engine books as possible before you spend a dime on parts or machine work. Know what you are going to do ( Have a plan) before you do it.
To bake a cake you have to know what ingredients you are going to use, what order to mix the ingredients and what proportions of each ingredient you are going to use. How much time mixing and baking.
And then it might come out the way you thought it would.
Just putting different ingredients together without a recipe will get you nothing but something to throw away.