Is it necessary to plug the holes under exhaust ports they have a ton of miles on them and they look to be plugged up with carbon? Customer is putting headers on......truck application. Thanks in advance Moparts.

You can easily run a tap into the holes and plug them with allen head set screws.

Ya...done that with some 86 360 heads with the same style headers.....but I thought that I seen where someone got away with not doing it. Anyways thanks for the quick reply.

Does anybody know what size tap and plugs you need
for this project?

13/64 and 1/4-20 iirc. EDIT 13/64 for the drill bit and 1/4-20 for the tap and plug. To plug it a 1/4 coarse thread stud with the female recess for an allen wrench to screw it in works good. Just pick the right length

Sweet.....thanks.

My 302s I did that, broke a Greenlee tap off in one hole, so be careful. Plugged all the other holes with some short bolts I had found in a parts drawer, plugged the "tap hole" with JB Weld.
10,000 miles later all are still plugged.

BTW, I used a rotary cutoff wheel to take off the bolt heads. May be cheaper than setscrews.

R.