2 barrel , 4 barrel, whose got the answer?

bear with me please: 1983 318 stock, in a b250 van (concversion). because it is a lean burn (that doesnt work any more) it ios being converted to a hei ignition system with vacuum advance ( the gm hei module). the present carb (2 barrel) doesnt have a vacuum port to run the vacuum advance. so the coice is to either replace the 2 barrel (2280 holley or carter bbd), pull manifoold and change to a 4 barrel, or some combination. in a ideal worl i would change to a spreadbore and run either a thermoquad or quadrajet (550 cfm). since i havent started taking anything apart im open right now to considerations. this will be low rpm use (4500), hoping to gain better mileage (arent we all) as well as more power.
to summereize.\, a stockk two barrel on stock two barrel manifold, a four barrel on that 2 barrel manifold, or a 4 barrel with a 4 barrel manifold.
interested in your thoughts if you please. i also appreciate your time in responding, thanks
palani