In order to curb detonation, you need to keep temps as controlled as possible.
Actually, this engine was zero decked for the 2nd part build which used closed chamber heads. And at .090 between the head and piston...you could have detonation during the hotter months.
I suggest milling the heads a bit less, and removing anything in the chamber that might be sharp.
I would also run a step colder plug than stock. And total timing should be kept to 35 max. This is if you live in hotter climates and closer to sea level. The higher up you go, the less it trouble it will be.
I also did not advance the cam...even at 9.8:1 so you have to be carefull what you do!!
Brian