So, a while back I had the exhaust put on the 81 with its 400. I did the rebuild myself using one of Tim's kits. The exhaust shop pointed out I had an exhaust leak from the front of my passenger side head. Like one of the accessory mounting holes had cracked through, or it was an old AIR port. Any ideas why that spot would leak exhaust? It's the outermost hole on the face of the head.

 

No ideas other than a crack, which Budmud has been fighting as well. Can you plug it using some PTFE paste and a bolt?

 

On the top corner of the head above the exhaust side, you will have the AIR injection system. One end of the head will have a threaded insert installed, this is where some front accessories bolt to.
The other end may have the same threaded, or they have a small expansion plug pressed in. This plug may be rusted out and leak exhaust, or it may be missing because the AIR was installed there.