I'm using Sunoco 93 which is the highest octane available where I live. Compression is 10.25 to 1. I'll try backing off initial timing and see what happens. I'll also try to locate a dwell meter and verify settings.
Start with the intial at 5* at whatever rpm the FSM says.
If you plot out the timing specs that DragonSlayer has kindly provided, you'll see how sensitive the timing curve is to the initial setting.
It's a very rise in the advance off of idle.
Also an older distributor its more likely the primary spring has a stretched a little. If you find the advance is starting at a lower rpm than is acceptable, put a little more tension on the primary spring. Test and measure first.
If you don't have the service manual, this will at least get you most of it.http://www.mymopar.com/index.php?pid=109
Should cover setting for dual points. There also may be a Tech tip on it.