As I was draining the coolant from the radiator, the bottom drain plug stripped, although the top air bleed plug was still in good condition.
I moved the good plug into the bottom and started trying to fit various bolts into the top air bleed port.
I found out that the top air bleed port is M12 x 1.25. (So is the bottom)
This is on an '87 N/A with stock radiator.
I found an oil drain plug (metal, 6pt., 14mm head and I think 20mm long) that was M12 x 1.25 at an Ace hardware store and it fits the top bleed air bleed port.
It doesn't sink into the port like the stock plug, but it forms a good enough seal on the outer surface of the port to hold pressure at normal operating temperature.

It was $5 and change. I think this plug is for a 99 Toyota Tacoma Beck Arnley P/N 0160116 or Dorman 090049 and is alot cheaper online.