>> The mechanical is set at 12° BTDC at idle and 36° total all in by 1700 RPM.>>

That is already a good amount of advance.

If there is a slight audible pinging when climbing a highway grade the timing “might” need a bit of tweaking.

I have run with an Actron ODB-I scantool hooked up on a 1995 360V8 and seen as much as 47 degrees of ignition advance at 1600 rpm on a level Interstate,
but the 1995 has Magnum high swirl heads, EGR and SMPI. I do not remember the manifold vacuum when that happened but would guess 10 to 12 inches of Mercury.