heavy bog under acell

Hi everyone, I'm new here to the forum.
About me: Dan from Massachusetts, Mopar or no Car. full time mechanic (91B) in the RI National guard. Been a mechanic for 12 year mostly working on fuel injection, have a Neon srt4 as a DD. Back in July picked up my first old Mopar a 73 duster 340 4 speed.

About the car: stock 340 from what I can tell ( vin on motor and trans matches car, )
Holley 750 vac sec 74 jets stock plate on rear .35 squirter, blue squirter cam, a weiand stealth dual plane
Stock electronic ignition, new mopar performance distributor, 16* btdc initial, vac advance connected to ported source, 5 pin ignition box, accell super stock coil, msd sf wires auto lite 65s at .040 gap.
8.25 open 3:23 rear
Hi po exhaust manifolds tti head pipes and x-pipe.

Problem: under moderate to heavy throttle off idle or at cruise I have a huge bog, if I ease into it no bog pulls good. At idle if you rev it no bog although it doesn't sound that crisp, a slight delay. I adjusted the carb with a vac gauge best I got was ~12 hg so I put a 6.5 pv.

What I've tried: bigger and smaller squirter, (clearance on linkage good about 0.015) different pump cam. Neither had any change.

My thoughts are maybe pv too low, timing or vac advance maybe, any thoughts or advice appreciated

Other notes:
When I got the car she had headers which were leaking so I swapped them out to manifolds. Since then the problem showed up, probably a coincidence.