'89 GT Oil Pump DriveShaft

The pump shaft is supposed to be installed from the bottom. That the only way you can install it with the washer on the shaft. The washer on the pump shaft is critical - it keeps the shaft from lifting out of place and falling into the pan when you remove the distributor. With the oil pump removed, the shaft is lined up with the hex hole in the distributor. It is installed with the washer positioned facing the bottom of the distributor. Then the gasket and pump are installed.

Notice the washer in the attached image.
View attachment 422570

No washer on the pump shaft - watch out, because the next time you remove the distributor, the pump shaft may ride up part way and then fall out into the bottom of the pan. There have been many posts asking for help to recover the misplaced pump shaft from the oil pan. Usually to get it out, you end up pulling the pan. Do it right the first time and this is never a problem.

I second that suggestion to install from the bottom and install the retainer collar. The min otherwise to get it back out would be pull the timing cover and fish from their.