440 detonation issue

first, try pouring Coca cola in it( I know, but the sugar seems to knock out the carbon better than water; Ever taste carbon? kinda sweet; don't ask).
You have vacuum advance? Plug it and test. My first bet in the dist, next one, after getting carbon out would be: then mix race gas in. My experience- ex wife started putting reg gas in my 10.5 340; broke a piston.
Or put more duration cam in it, to bleed off compression. I needed to get a truck out of my way; I put a low comp 340 in it, with a middle purple shaft cam. It jumped all over the place at idle, but started moving at 3000 rpm. Killed every 5.0 mustang it saw. It would finally catch up at top of 1st gear, then jump 3 car lengths.
Check for total in the dist, with vacuum, then decide.