I'm no carb man but here is my take on the dual carbs from Langdon. Looks really cool and that is the best part of it. Probably is also the the "why" part of it. You must remember that what he sells is the two bbl Ford Escort carbs that have progressive linkage so they are running on one very small primary of the carb as Escorts were 4 cylinder engines. I've got this setup and I wouldn't do it again or necessarily recommend it unless you like the look. Mine runs fine but it would run fine with only one of these carbs and perhaps even better.
As for those 4 bbl manifolds that is pure bovine droppings. But COOL as Hell. But not to frett...Tom Langdon will do a selling job on you and you'll come away convinced it is the perfect setup. Ask me how I know..
Bottom line: it's your truck/car and your money.