Tap it and put a small allen set screw/plug in it. (Use Loctite) That's the way I do all mine. I don't think I would trust just stuffing JB Weld in it because of the heat, fuel, pressure etc.

If I remember right, the hole is already the right size for the tap so you don't even have to drill it, but I can't remember the size. 8-32?

I don't believe it is a compression release however. None of us are sure, but I think it is kind of an Exhaust Gas Recirculation port for smog purposes.

AV8TOR