I'm almost done throwing up, just the dry heaves now.
My post mortem is very similar to yours Lee. Given the amount of gasket sealer that the previous owner had used at the front of the oil pan, its clear he was chasing a leak of some minor magnitude. I came across the leak and in trying to fix it, I made it worse.
There is one broken shard from the right hand side of the end cap, the left hand side is just showing two cracks. I highly suspect these are of my doing when I tried to use a tap and then insert a larger sized bolt.....shame on me for being so cavalier.
The side that has the chunk missing is right up to the timing plate, so I suspect no bolt/nut combination is going to be able to fully cover it up, thus continuing the leak.
This seems to leave me with two options.
Option 1 - attempt to repair with the engine in the truck. Removing the end cap and attempting a repair via tig welding.
Option 2 - take the engine out of the truck and take the whole thing to a shop for removal of the cam shaft the right way by removing the valve train, push rods and lifters. Remove the timing cover plate, clean up and replace the gasket between the block and the plate. Then replace the end cap with one from the Unobtanium Store and have the engine shop put it all back together.
Sorry, I went back to throwing up.
On a related note. When I lifted the engine an inch this morning, back in the good old days before I knew how badly I screwed up, I lifted up the motor mounting plates that you can see in this photo.
The sheet metal plate does not seem to serve any function and is considerably wider than the bolt holes in the cross member for the motor mount bolts. I suspect the 1/4 aluminum plate was used to allow the motor to be height adjusted properly. My question is does this plate serve a purpose, because in fact, it makes getting to the front of the oil pan a bit harder.
Now I will get back to my form of meditation, which involves cleaning up the shop.