What carb for my 340 build?

That HR carb has made in China parts on it. If it says Quick Fuel on it, it’s China made.

If you look at the venturi sizes, QF’s CFM ratings don’t make sense.

The carb you are looking at has 1.375 X 1.687 sizing and they call that a 750. And that’s with a choke on it.

The Brawler is 1.390 X 1.687 and it’s called a 750. An .015 venturi size difference may not seem like much, but it’s a pretty big jump. And the Brawler doesn’t have a choke.

Like I said...with the single plane intake and your gearing I’d use the smaller venturi carb. You won’t lose anything on the top and driveability will be better.

Unless this is a street only car the choke is useless. The choke is the single biggest piston ring killer there is. These engines only need a very rich mixture for the first 10-20 seconds after fire up. Any longer than that and you are using excess fuel that does nothing but wash the oil off the cylinder walls and increase ring and bore wear.