My 340 getting 6 mpg

340sFastback said
With manual trans I would go Holley double pumper. Maybe compression test and hook an air/fuel ratio gauge up see whats going on. Lastly go new carb not some old unknown carb.

I've been using the older version of this one for years (love having the choke on a street car, but I do live in MN :lol:)
Holley 0-4779C Holley 4150 Double Pumper Carburetors | Summit Racing
Quick Fuel BR-67213 Quick Fuel Brawler Street Series Carburetors | Summit Racing (cheaper but only comes with electric choke)

Nice car! Best of luck on whatever carb you choose.