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...
I have the disc brakes from a 73 dart I want to swap on my 66. I'll use the upper and lower control arms and spindles but what about the tie rod ends? Do I use the 73 tie rod ends and adjusters or will the 66 ones work?