Was there originally any type of sealant at the engine tin where the various pieces overlap and screw together? I removed the front left piece near the alternator and it looked like it had an old bead of sealant where it overlapped the next piece. Could've been done by a PO? Or original?

I think it may be a latex type caulking.

The majority of the motors I've looked at / taken apart have not had any sort of sealant. So by the numbers, I find it unlikely that there was anything there from the factory. The stuff that I have seen on a few engines is more of a foam strip than a 'goop'.

There IS a foam strip that was used on the sections that overlay the cooling box (or whatever it's called). Naturally, it disintegrates from age & it was very thin. It'll take some searching, but replaced mine with factory pieces in the late 70's & kept the parts labels. That's the only area that had it. All other pieces simply mated painted metal on painted metal.
Pat

Now that I think about it, you are probably correct about it being a sponge tape. That is probably why they corrode so badly; foam retains water.

Yeppir!

But when it's young & not subjected to too much moisture it does its job - cooling!

Sponge tape isn't really correct - it was just a length of sponge-type material (maybe still is), without adhesive on one side. I suspect it was jammed in as the pieces were torqued down. At least that's what I did with mine (no adhesive). You can easily reproduced this at any hardware store, though it will probably have adhesive on one side.