Dear Mr. Dbane;
The 3 pot manifold with 2bbl adapters is a good idea. I've not done it, but plan to on my 278". As mentioned; there's constant adjustment on the linkage if you "stab it" often, but thats Hot Rod life.
The Clifford with a 390 CFM Holly is good too as you avoid all that adjustment (saving fuel) & only lose a little power.
With $3.00 a gallon gas It's a "toss up". The single 4bbl is probably the cheaper (purchase/operating) choice, all things considered.
How you plan to drive it will be the determining factor I feel.
BTW: Manifold vacuum is equal throughout making the 15% lean (end cyl) a myth.
Good luck.
