Doesn't really matter if its stock or built, really doesn't even matter if its for an LT1 or even a GM car really...

Flat out whats the best plugs to use... power vs dependability of course is going to vary greatly.. but that is all a matter of style really

 

I ran Autolight 103's in my AFR heads till I figured out I'm supposed to be using a gasketed plug, not a taper seat. I now use the NGK BPR8ES plug. I didn't have a problem with either one.

 

It's my understanding that the Autolite 103 is 2 steps colder and the Autolite 104 is 1 step colder. I've run both these plugs with good results.

 

I would guess that using a iridium tip plug wouldn't be a good idea with FI? Kind of like you don't want to run certain kinds of plugs with the spray because it could melt the tip... if I'm understanding plugs correctly.

 

I've run tr5 & tr6, now, a zex plug. The zex plug has not fowled. I've since leaned out the WOT AFR/ and, low speed closed loop AFR. I purchased a spare set.