292 I6 tuning help needed

[RThree]

Alright guys I need some more help with my (mostly) stock '72 292 this thing gives me fits….

To main symptoms:
-Rough surging at idle until it stalls, but runs decent at higher RPM
-timing has to be advanced to 15+ deg to run with out backfiring though the carb when given throttle and have good throttle response (4+deg is default)

We have done the following:
-Verified TDC timing mark is correct on harmonic balancer
-Compression check is consistent across all cylinders (140psi + or – 10psi)
-Replaced points distributor with HEI and ran an unfused power source.
-removed intake/exhaust manifolds to check for cracks none found. Machined mating surfaces and replaced gaskets.
-Installed a new Rochester 2GC with an 2-1 bbl adaptor plate
- Set timing to default 4+tdc but idles rough and backfires though the carb with throttle.

Any ideas?

Thank you for taking the time to look this over. Please let me know what other information would be helpful.