Upgrading my 340

Raul, unless the headers were specific for a 273/318 app, they are most likely off the shelf 1 5/8" jobs. You do not need more header than that to go faster than you are, I did a
set of T/A heads on an AAR 'cuda, 340 6pak, Mopar's 292/.508 purple shaft, cc'd @9.69:1 compression. These were not "all out" ported by any means, the car is full-on street
& the only change at the track was bolting on the slicks. With a 9.5" converter &727 trans the car has gone a best ET(I believe 4:30's)of 12.35, & a best MPH(4:10's) of 109.
On a set of off the shelf Heddman 1 5/8" jobs, 3" pipes & muffs, dumping in frt. of the axle. Your ride should be lighter, & that cam should have more torque, the stock T/A rockers
on that 'cuda were only netting .475-.480" lift worst to best. I would check Your timing curve & jetting & go from there.....