Your carb and intake are your problems.
A holley 750 is too much carb on your 340. The torquer 340 intake is garbage at best. I picked up time replacing a torquer with a stock 340 cast iron intake. Your combo wont like a single plane intake either, get an airgap and a 650 and you will pick up...
Bad season, I worked too much.
This winter:
Car 1 will get a new engine and trans, bumper brackets installed, interior recovered, and exhaust tips
Car 2 will get the front bumper rechromed, and the clutch pedal modified
Car 3 will get the rear springs replaced, radio, and center console...
3430 race weight duster, SS springs, 3.91 gears. Stock 340 rotating assembly, stock X heads, comp hydraulic cam, eddy air gap, holley 650 carb, stock distributor, firecore wires and a PTC 9 inch converter. Best of 12.40 108.98 uncapped