Engine: Missing Fastener?

When Christopher Markley delivered our completely rebuilt SS engine he told me there were two items I'd need to look into. We'll talk about one now. There is a hole in the engine case that looks like a fastener should be used to seal it, but when Christopher investigated the parts diagram he saw nothing. Also, it did not appear to be threaded. Pictured above are my spare cases, with the same hole, but this hole is threaded very finely; therefore I am assuming something is screwed in there. I am pointing at the hole for your reference in the picture. Please post a comment and let me know what belongs in there.

Once I find out what screw goes in there, I can clean up the threads and put the correct fastener in place.

Thanks in advance for your help.

FOLLOW-UP / LESSON LEARNED:
This is where the junction box goes. (Thanx Paul)
Here is a photo of the stock junction box for your reference.