I apply some red rtv to the threads on a short bolt and screw it into the tapped hole, just as others above have stated.

Here's more discussion on this topic from the Team Chevelle Website:

Originally Posted by Dean;2841745
A long enough bolt through that hole acts as a set screw into the side of the fuel pump push rod to hold it UP while changing the fuel pump.
Just don't forget to plug the hole with short bolt when done.
I bought a pickup one time that had nothing in the hole and oil was being blown back all over the motor by the coolant fan.
Links here ----> thread link photo

In the Stovebolt Gallery ~~ "The Orange Crate" 1965 C10 SWB Step Side Build Thread

Inspired to be different. Different in a way of my own, not in a way that others strive.