I have one of those manifolds on a spare engine, so I know what you're trying to do. Have you tried calling Clifford for some help on it? I don't believe it was ever really intended to be hooked up to anything. If it has grooves cast into the floor, you may want to grind out the center area under the carb so the middle cyliders don't run too lean.
For 55-62 cars with hood clearance issues when going 2x1, there are other carbs, like the Holley one bbls used on Ford sixes which are much shorter. I believe carbs from a slant 6 were shorter also?
Comparing a 4bbl to the rather tiny H/W, I'd say yes, the 4bbl, when properly adjusted, will out perform the H/W regardless of camshaft profile. The H/W is fine for normal driving around town and under 3000rpms. Talk to Langdon about it.
You didn't say if it was a stick or automatic, but if its an automatic, you will want to stay conservative with the cam profile, something like the dual pattern cam that Langdon sells. better to just stay stock based on your intended usage.
