What are the visual differences between the two. I searches for ever and cannot find a decent thread with pictures of a s5 NA trans. Plenty of s4, but some of them look different. Pardon my ignorance I'm a FB guy.

 

I've seen a number of different case styles. The easiest way to tell an S4 transmission from S5 is the mount. S4 y-brackets attach with 2 bolts on the bottom, while S5s use 4 bolts on the sides. https://www.rx7club.com/2nd-generation-specific-1986-1992-17/gearbox-mount-issue-950258/