figuring out advance timing

Backally said
Right now it seems to like 13.5 idle, 13.8 cruise a/f. I started the cruise at 15 and it felt like it was “trailer hitching”. Couldn’t hear it, but I could feel it. I dropped the a/f .2 at a time, the 13.8 feels the best.

The AFR you are zeroing in on are in line with what would be expected from a hot rod.
Here's the real deal Desired Carburetor AFR Characteristics At Different % Load (just close the pop-up if tapatalk asks you to join)
The one caveat here is to be somewhat skeptical of the AFR interpretation by the wideband O2. Will get back to the is in a minute.

Backally said
Right now the cruise timing is at 36, I am trying to introduce more of a vacuum advance in that area. From what I have read I should be able to add a good 10+ degrees of timing into that area.

As Jos mentioned factory Chrysler engines added enough advance under light throttle conditions to bring the timing into the low 50s BTDC. Thing is now you have a different stroke ratio so I don't know how that all plays into the dwell around TDC which in turn has some effect on ideal timing.

Backally said
it cruises between 35-40 kPa (converts to 10.3-11 hg). This is cruising at between 2500-3000 rpm, which is from about 50-60 mph

Frankly that seems quite low. If its really that low then fuel distribution is going to be poor and the mixture will want to be somewhat richer. Richer mixture will burn quicker than a lean one, so less timing is needed.
Timing advance guru input needed

The reason to be a little suspect of the AFR number is the WBO2 interpretation is based on the assumption that the combustion is uniformly completing in the predicted way. With the low manifold vacuum that's fairly unlikely.

If you're interested in the in depth version, read here
Motorsports Village • View topic - How a Wideband gets tricked to read wrong AFR