best carb for 340?

The same. The TQ is a good carb, you just have to play with jetting. They lend a better throttle response than other higher CFM carbs on an engine that size, because of the small primaries. Not very good race carbs, IMO, compared to a DP but excellent on the street.

Rumble is right on the money, with the tune.

I used a Street Demon, same idea, new components, so you can get jets and rods easier. It has a nicer idle system with the sandwiched baseplate gaskets and the thin, metal spacer that it comes with, in conjunction with two bleed holes at the front of the primaries, that redirect air to the center of the intake plenum to help idle and transition stability in RPM. It certainly does what it's designed to do. I was able to trim 30rpm on my digital tach from the idle with that carb.

I'm using the 625 on my 318. They do make a bigger one. The AVS that rob suggested would be very similar, but the primaries are a little larger and it has smaller secondaries. More of a square size. the Street Demon acts like a TQ, but is on a square bore intake pattern, unlike the Rochester and Carter carbs. Accomplishes the larger secondary flow like the TQ, with a unified secondary throttle plate they call a goggle valve. They did that for the same reason they did the air bleed at the primary, to help redirect air to the center of the intake plenum.