Ok, tore it down to the bare case. Man, that was easier than I recall. The stock CPU spec is an Intel 486SX25, but I can't tell... I didn't think the slower 486s had coolers on them?

Also, my CMOS battery leaked, and it's one of those barrel types. Think it may have screwed some traces up. Think I need a new board?

Desolder the battery and start cleaning it up with some mild cleaning solution (vinegar, dilute baking soda, or weak IPA for instance). It's hard to tell how much damage there is just from the surface, although it appears some traces may have failed. This is fairly easily repaired using fine wire to bridge between vias, but it's up to you whether you want to undertake the project.

Shame about the battery. Hope you decide to fix it and get it running again. The PCI bus would be a pipe dream, as you would have to have the proper chipset on the mainboard to support it. Our first family computer back in early 94 looked to be this same system. Had 486sx-25, 4mb ram, 210MB HDD, and from the back picture you posted, looked just like that. Same soundcard too. You don't have a front pic of the system, but ours had the 2x panasonic cdrom instead of the 5.25". My dad kept that machine til sometime in the early to mid 2000's and finally tossed it. I am kicking myself for not taking that machine now. Logged a ton of hours on that thing tinkering.

That CPU is not a 486SX-25, it's a Pentium Overdrive (the 63MHz version if I'm not mistaken).

Correct, his had been upgraded at some point, but he mentioned it came stock with a SX-25