At TDC is an s13 distributor rotor button perfectly horizontal and an s14 slightly up from horizontal?

Nope they point in the same place its really the exact same engine. ka24de is same as all the others. a ka24e would be a different animal.
I know that to put it a tdc it does not point at number 1 but a bit after it. I will probly be corrected on this but the spark takes place before the piston reaches tdc. So when you put a distributor at tdc. The pointer is like the next tooth past number 1.

I always just google (ka24de tdc) click images.

This might help.

240sx-distributor-timing-t161707.html