Do you know what this is??

[Capri306]

The ports at that point have NOTHING to do with EGR. They are air injection reactor (better known as A.I.R.) pump passages, designed to add fresh air to the exhaust stream in hopes of completing oxidation, and to aid the catalysts. Air is only pumped into these "upstream" ports when the engine is cold, up to a predetermined temperature and time. This is what those "bumps" in the exhaust ports are for, and that longitudinal passage going the entire length of the head is simply a common manifold for all of them. If you've ever had the joy of replacing air tubes on a small block Chevy, now you know why Ford did it better.

Okay, enough of the education on emission controls. You're gonna hafta plug that hole with something if you're not running an air pump. I'd suggest doing something like most guys are saying on here, and create something that's going to thread in there and plug it as well.

By the two pictures, it appears that this is a 90 degree elbow with a bolt through the center attached, correct? If this is the case, a large fender washer may do the trick, otherwise mebbe you can fill the end of the tube with welding. DO NOT be tempted to use something cheap and easy like Liquid Steel or JB Weld, as they WILL NOT work for long. Find a friend with a MIG or even a flux-core wire welder and fill up the center on the end of that piece.

FWIW, this is pretty unique looking, even for a 1979 piece.
BTW, find some different heads. Experience with 1978 heads speaking here.