Vacuum advance tuning to maximize cruise MPG?

I took AJ/FormS advice and made some changes. The adjustable timing box I got does not work so I'm doing this old school now.
It was 80+ temperature today so good for a normal tune today.

I started with setting initial timing with a vacuum gauge at idle and ended up with 24* 16" vac. Instant start even after heat soak. 13.1 AFR in neutral.

11* mechanical advance all in by 2300, Total mechanical = 35*

Drove the car without vacuum advance 13.9-14.3 AFR cruise, 12.3 WOT and had no ping. Bumped up total mechanical to 38* and had slight ping. I put it back to 35* total.

I decided to work with ported vacuum; lack of engine brake decelerating with full manifold vacuum and manual brakes is annoying. I had an 8.5R vacuum can and ground down the mechanical stop on the lever. I adjusted the can to start moving at 8" VAC and is all in at 15". I drilled a hole in the distributor housing and tapped it for a 4-40 screw. I'm using this as an adjustable mechanical stop for the vacuum advance plate. The screw does not interfere with the cap and is easy to reach with the distributor installed. See pic.

Total timing with vacuum advance for now is set at 45* Drove the car in cruise mode; 45-70 mph and once I'm at steady speed I'm at 18-19" Vacuum, 13.9 14.3 AFR. No ping with hard acceleration.
Tomorrow I'll slowing adjust the vacuum advance max limit and see how the car reacts.