318 carb questions

First off, I apologize for this question and the no doubt countless others in going to ask in the near future. Besides changing spark plugs, filters, and oil, I've never done anything (nor do I know anything) about engines. But I'm excited to learn.

I'm finally getting down to taking apart my 318 to, at the very least, replace some gaskets and the carb, and most likely the heads. I've decided to keep the 318 for the immediate future.

The car (68 Valiant) already has headers and duals. My first instinct is to swap out the 2bbl for a 4bbl, but after searching around it seems like some folks are saying it isn't worth it. So question 1 would be, should I go 4bbl or a newer 2? If I decide to go with 4 do I have to get a new manifold or will the stock one work?

TIA