my thoughts are to KISS on the whole thing. you already have the pigtail/whip for the electronic ignition, why not just get a stock electronic ignition distributor (non lean burn edition) and snap that puppy in. then just plop on a carter BBD and be done with it. it's basically factory, you'll need to modify practically nothing. all of that stuff is cheap and widely available.
going from a 2bbl to a 4bbl will net you more power but likely at the expense of fuel mileage. and the power may not be where it is most useful or useable for your application. i'll agree a dual plane with a small square bore or a spread bore tuned in nicely is a hard combo to beat, but you're gonna have to work to get those mpg numbers. also, i wouldn't put a 4bbl on a 2bbl manifold; except for rare instances it's just a solution to a problem that nobody really has.