Ford 5.0 experts - help identify part

I was putting an 88ish 5.0 Ford engine into a project truck today when I heard a rattle in the oil pan. Upon removal I found this mystery part in the bottom. Anybody know what it is?
 

1/2" socket for size reference

Fits on the oil pump drive shaft.

Cousin_Eddie (Forum Supporter) said:

Fits on the oil pump drive shaft.

Thanks! I'm assuming on the pump side. Think I can slide it back on if I pull the distributor? 

Correct on the oil pump driveshaft keeper.

No on sliding it back on. It's designed to keep the driveshaft in place when you remove the distributor. You have to drop the pan and pump to put it back on.

Be very careful when you pull the distributor next time, because that's what keeps the shaft from popping out of the pump.  And that involved patience and a magnet, or dropping the oil pan.  Either way involves swearing.

You need an entirely new oil pump driveshaft if you ever pull the distributor.  If you pull the distributor, the entire shaft will drop into the oil pan.  Then you need to remove the pan and oil pump to replace it....  don't ask how I know. 

I already dropped the pan to get the retainer out, so I luckily I'm mostly there. Tomorrow I'll pull the pump and get it back on. 
 

Thanks for all the advice so far. 

In reply to WillG80 :

I'd replace the shaft.  I suppose you could put the retainer back on and hope, but it will likely slip down or off again and it could break at the pump.  The replacement shafts have a welded ring.  If you weld you can tack weld it back to the shaft.  It goes at the top right below the hole for the distributor.  It's sole purpose is to keep the shaft from falling out when you lift the distributor.  Honestly where the shaft is now if the pump and distributor are installed, it's a useless piece.