Rowdy /6 Timing Curve Recommendations

Timing at full load (such as wide open throttle 3 or 4th gear on a high compression, cammed engine does relate to octane. People will call the situation octane limited. In other words the combination could take advantage of a higher octane fuel if it was available. But if its not available, then the timing under the high load conditions has to be reduced.

Low rpm 'All in' was something that made sense when drag racing and using points. The same concept applies with electronic ignitions with the caveat that high rpm retard will occur if its not compensated for in the distributor's advance. (There apparently are now ways to compensate in the control electronics but that's not what you will find in the ECUs available for your project). The higher the engine rpm, the worse the problem. At 5000 rpm it might be 1 or 2 or 3 degrees. At 8000 it could 4 to 8*.

However you wrote this is a street car, so this changes the story even though it will see some strip use (my understanding).
1. The engine will get heat soaked when used for trips longer than 1/4 mile each way. ;) An hour or two driving is what the timing needs to be set up for.
2. Vacuum advance will eventually be used. So while a fast 'all in' is usually fine with no vacuum advance, once the vacuum advance is taken advantage of, the 'all in' early curve will result in way too much advance for cruising and moderate throttle around town and even on highways.

I would start with the slant distributor you have.
1. Measure the timing vs. rpm from as low of an rpm as you can, to as high an rpm as you feel comfortable. You'll need timing tape or a dialback light. Timing tape is better. And tach of course.

^This is now your baseline^
You know how it performs, and if you haven't yet, measure how much vacuum changes the advance. That's also a part of the baseline.

Then make one change! The simplest will be to increase the initial timing and reset the idle speed to the same as before. See if it is as strong when you slip it into gear. if you need to rev the engine more so it doesn't stall, note that. That's a step backward. But keep going with the test. Drive it and see how it tolerates or likes more timing cruising at different speeds. Also test WOT in 3rd or 4th and if there is any detonation (ping) back off. Again, take note. If you have to put that off until the drag strip opens, so be it.

You can also change when the advance begins. That's a little more involved. I don't think you'll have to do that with a mopar distributor and a manual transmission.

IMO the Mopar distributor advance is superior to the MSD. It can handle a fast advance off idle and then slow it down when combustion efficiency picks up.