Sent another technical request message to Holley/Mallory regarding service.  First was ignored, but this time I also asked for referral to any private party that specializes in vintage Mallory distributor setup.  Maybe someone there who still has connections to retired staff with that knowledge (?) will take pity on me.
While my customized OEM Loadomatic (dual points, altered Offy advance limiter, lowered spring tension, etc.) & Pony/Holley 4000 combo is still running very strong, the reduced gas mileage IS finally enough to prompt me to put the NOS Mallory with mechanical + vac. advance into service (I also have slight ‘rough-running’ when cruising in 3rd OD at low RPMs, but that might well be merely a carb adjustment issue?). Otherwise, I might assume that the vintage unit, as-produced, was designed to be a ‘drop-in’ aftermarket performance upgrade, and was likely to be originally setup correctly as such at the factory, with street-able advance curve & point gaps, so a good soaking in automotive electronics solvent (and re-lube of the advance mechanism) should  be adequate for testing. I’ll put it on the SUN machine first and see what’s what before I cut off the ends of my plug wires.
If I’m lucky, I’ll be able eventually to get some useable vac. advance in combination with a modern carb also (restricted port vacuum?).  Whatever.

6 VOLTS/POS. GRD. NW INDIANA