This piece of plastic just cost me 3 hours:
So there I was, re-attaching everything at the rear of the engine, and everything is going well. At least as well as can be expected when you are under the hood and kneeling on the engine while trying to work. With all of the down-low-and-in-the-back stuff done, I moved on to the re-installing the distributer. After all of my hyper-caution about timing and all that affects it during this whole job, I'm about to verify that all is indeed good.
Full stop.
The distributer will not go down into the engine the final 1/4".
WTF?
So I second guess my self and pull the valve cover again and re-check TDC. Everything is fine.
Again, WTF?
I remove and re-lube the distributer and even try to fit it in in ANY position (it should slide in in two positions 180 degrees apart). It won't go in. So I pull it back out and set it aside, grab my penlight and shove my face up against the firewall so I can look down the distributer hole to see what's going on. Down there, in the black abyss, leaning against the oil pump rod, is the plastic bit pictured above.
OK, that has to come out.
But just how in the hell am I going to accomplish that? That thing is way down deep inside the newly-assembled engine. After trying to catch it with a long screwdriver, and failing, I devised a new method. I clipped off a piece of electric fence wire at about 2' in length and created a hook at the end. Then, with my face against the firewall, my knees on the engine, and my butt in the air, I grabbed the panlight with my left hand, and the wire with my right and somehow managed to snag the offending part. Holding my breath, I then carefully extracted it straight up and out of the engine. I could easily have fallen-off and into the lifter valley where it would be unreachable without pulling the intake all over again - but I got lucky.
Whew!
So then the mystery of what the hell this thing was, and what (if anything) it did as part of my engine, became my new concern. I sure didn't want to open the engine up again, but if this was a critical part I didn't know about, I wanted to get it to where it belonged. It didn't look like anything I'd ever seen inside a Chevy V8, but I needed to be sure. So I jumped into the wagon, and paid a visit to the local Chevy dealer. No one could positively identify that little, white,PITA. But both the mechanic and a group of parts guys agreed with me that it didn't belong anywhere near where I had found it. Good enough for me. What a bizarre sidetrack this has been for my project. I still don't know what the thing is (our collective best guess is a valve seal), but it seems it was just some automotive flotsam a careless mechanic allowed to drop into the engine at sometime in the past.