If you run an aftermarket ignition system like an MSD, you can get a timing retard box. They are generally used for NOS or other performance adders. But if you set the retard for say 3 degrees, and you run the retard box on a switch, you can switch between your 33 and 36 total timing to match the fuel you are running.

Yellowbird, I know you don't want to use an aftermarket ignition, I am just illustrating it for others that may. You can set these boxed to only adjust after a certain RPM (whenever total time is engaged due to distributor curve). Initial timing is only a number to get you to your total time.

I'm not certain if this is possible, but ideally, instead of a box to retard the timing, you would want it to advance the timing so you could always set the intial low and have the box advance to the 36. This would help in engine crank especially at hot temps.

My $0.02. And my intentions for my car after I get around to the time and money for a rebuild.