Are these Alum. or cast heads???
If alum, ignore the rest
If they are cast and you have a true 10.5:1, you will have to pull some timing.
That is too much compression for pump gas and cast heads, especialy if those are reworked stock heads, they have a poor combustion chamber design are prone to detionation.
You can try some colder plugs, set timing too about 30-32 total and add a little fuel.