I helped my Dad once with an old Ford Van which had a 6 cylinder inline 240 ci engine. He got parts from an outfit called "Clifford Research 6=8". He just wanted some more bolt on power and what he got was a dual carb intake manifold and a dual exhaust port exhaust manifold. He had to get a second carb just like the original and we rebuilt both of them for the project. Then everything was put back together The engine "breathed better" and had more pep, but it wasn't until he played with the distributor "advance" mechanism to take advantage of what the improved breathing could do for the engine that he got results from the old Van.
His motive for doing this was he liked to go up into the mountains of North Carolina, Virginia, and West Virginia
to go hunting and fishing and the original engine just didn't seem to satisfy him on those trips. Before he was done with it he had installed an Bendix fuel pump at the fuel tank and ran oversized fuel line to the two carbs.
On the flat highways of North Carolina there was no problems. But when loaded and headed to the mountains there just wasn't enough umph.
Dad never saw himself as a "Hot Rodder" but was inclined to speak of "volumetric efficiency".
This is a Clifford dual quad set up for a 6 cylinder engine. Just to show you an example of he stuff that
they made for hot rod 6's.
But he got what he was after with the modifications and was always willing to show and tell with other interested people. On one of his trips he found a guy who was so interested that he sold it to him.
He then purchased a newer van with a V8 and never had any complaints after that.
If I were going to be operating between long haul flat interstates and going up into the steep mountains,
I think I'd look for the Ford Vans with the V8 460 ci engines. I just think those cubic inches are hard to beat.