Vacuum advance tuning to maximize cruise MPG?

Looking to optimize the vacuum advance for max fuel mileage at highway cruise.
I'm thinking I need to install a vacuum gauge and tune to max vacuum at cruise.
Would like to hear from folks who have gone through this procedure. I'm not sure how far to safely push the advance up.

My setup:
73 Dart Sport 340 rebuilt with old TRW forged pistons 9.5:1, J heads, 270H cam, 727/3.23/29.1" rear tire/2600 RPM @ 70MPH
71 440 TQ dialed in with 14.5 - 14.8 AFR at cruise. Functional dual snorkel scoop with air cleaner sealed to hood.
Old MSD 6A, Autolite 65 gapped to .045, OEM dist recurved with welded up advance slots.
Current Timing at crank 24* Initial, 34* Total Mechanical
Vacuum Advance 14*@14" Vacuum advance can connected to full manifold vacuum.

I run 93 pump gas and have no ping or starter kick back. Touch the key and the car lights off immediately cold or hot.

Thanks for any input.