What plugs are You Running in Your 408 Strokers.

How hot is too hot?
Check the discoloration on the base ring and count the threads of discoloration.
Timing, the strap, wot? The deepest portion of the insulator...and on n on.

I ran those gr4gp .030 quench with iron heads, 9.98 comp and 8.3 or so dynamic and 28 total timing on 91 chevron.
Did the testing and checked everything to know.