Detonation on 408 Stroker

Hi All

I have a 73 Duster with a 408 Stroker.
Ever since it was built I have been having detonation (ping) and running on when ign is killed.
I have gone through 3 different ignition systems 1) Original Mopar 2) MSD 3) Pertronix
It works much better with the Pertronix Billet Distributor than with the others, and by tuning weights and springs in the dizzy it is almost there.
Timing is 33 degrees all in.
Compression is 10.3:1
Heads are Mopar Performance cast ones.
I use 99 octane fuel always.
I have tried several different heat range of spark plugs
It has a Holley red Top fuel pump
Now I only get ping at WOT, even 3/4 is fine but as soon as it is WOT it pings
The carb is brand new Holley 750 vac sec, and has not been touched, so I'm wondering if this may need different Jets / accelerator pumps etc?
The car also tends to run on of I turn it off in Park, if I shut it down in gear, where the revs are lower it is usually ok
Thoughts / opinions welcome
Thanks
Kev