[fastd]

SBSerpent,
Did you search for Sunoco race fuels gas stations specifically? Also, you may be able to find some race shop locally that sells higher octane fuel.

I had the same issue: phenolic spacer helped a bit; when I added fuel injection it fixed it; I’m sure the return line helped. You could add a return line and spacer, find some place to add 5 gallons (or more) of race fuel to a tank.