170 or 225 for super 6 build?

Road-ability is pretty good. Best economy I got out of the Hooptie was with a Holley 390 and 600 4160. (About 23 with either.)
Steet-ability is great if your looking for zap. The 390 will deliver liveable economy. The 600 will not get good mileage around town.
The 390 is a bit easier to tune in than the 600.

Better yet is the Carter AFB. It pretty much just bolts on and goes. Same with the Edelbrock. Pretty much the same thing.
Economy hasn't been as good as the Holleys. But I did a bunch of stuff to the engine to take those five seconds off at the strip. Apples and Oranges you know.

That said, with the Holley 4 bbls there is a bunch of jetting and general bandaid-ing needed to get the mixture right in all modes. Jets, power-valves, secondary springs, secondary idle setting is a skosche off factory, pump cams, and shooters. It takes quite a bit of work to get the A/F meter to read on the gauge, much less in the middle.

A BBD that is the correct one for the slant six is, of course, much easier to deal with. It's already set up the way it needs to be.
There is a bunch of messing around with BBD's that were used on v8's, and I wouldn't even bother with the Jeep units. Too many differences.

I don't daily drive my Valiant with the Carter 600 on it, but I could in a pinch. I'll probably convert it back to a 500 shortly. It's harder to keep the mixture right with the larger cfm boosters in there.

With any 4bbl, to get things working right, the distributor curve needs to be re-worked. There is no real advantage to a 4bbl until you get into the 9:1 range with compression and do something about the 170 head bolted to every slant since day one. :D

CJ