I need exhaust advice.

I know this is for "A" bodies but I needed to put a transmission in my 1988 dodge RAM truck. The old 318 had several oil leaks so why not do some freshening up. I noticed when I removed the exhaust manifold to repair some broken studs, that there are 3/16" holes below each exhaust port. One of them is open and it is at least 1 1/2" deep. The other three on the passenger side are plugged tight. I looked on my old 318 sitting here ready for the dart and there are none on it. What are they for? Can I drill them out? and how do I keep the carbon from going in and building up for that matter. Are they for the heat regulator? Maybe 1988 is too new for me to be working on!
Thanks!
Dartnabout