headers for a 77 360 in a 72 dart

Assuming they aren't clogged shut, you can plug the air injector holes under the exhaust ports with small allen head screws, or epoxy. If somebody is running later heads, say from the mid 80's on, with the air injector tube ports on the rear of the heads, I plugged those by taking a short section of the tubes, beating them flat and having them brazed to make sure they didn't leak. Can't remember if they can be plugged with small plugs mine was stil in a 88 D100 when I did it.
Hope this helps,
Alan