Slant six single, to slant six double.

Princess Valiant said
Once you get into machining and cams, you're also into a ton of money.

I had the best luck with a stock cast iron 2 barrel manifold and a 2 barrel carb from a 318. Peppy and on the cheap. Slightly improved mpg and way more responsive throttle.

Machining is nice but it's expensive and these days good machine shops are rare so they can charge what they want.

I have seen quite a few 2 barrel setups come up for sure.

It does cost, for sure. That's why I do everything I can for machine work here at home. I can enlarge spring pockets, knurl guides as long as they aren't real sloppy, install cam bearings and freeze plugs. I can also check for cracks. I can also do very basic valve jobs if the valves and seats don't need grinding. I've been looking at valve and seat grinders, though.