I'm a 60's 70's drag racer and was skilled in ignition and carburetion. You can run into overheating with both under and over advance situations. My '69 Z-28 Camaro ran best with 16 deg. initial timing and 36 to 38 degrees total timing... all in by 2,600 -2,800 RPM. the vacuum advance was very limited to probably less than half stock and coming in late rather than early. I don't remember how many deg. I limited to but it was very limited with the higher initial and quicker curve on the advance.
5* initial with no vacuum advance is seriously retarded timing. If I remember correctly the big block could handle pretty much what the small blocks could. Set that distributor up with 12 initial and 36 total for starters at 2,800 RPM, maybe bump it up 2 deg. from there. Take you vacuum advance arm and limit it to less than half its normal travel, or find an adjustable one and go from there. You probably will need a shop with a SUN distributor machine... must be an antique by now.
Good luck and have fun... keep the octane up!
Gerd
