As far as AT cases go, I may be able to help. I have about 4 in decent condition (aside from the typical yellowing). They also have working AT power supplies which I've tested - although I can't give any guarantees for longevity. As for RAM, I've just sorted them in boxes by type. I haven't separated them by speeds or exact types or sets just yet.
Sorry, no Intel DX4-100s or Overdrives, except a single AMD DX4-100 which I've tested and appears to be fine (I was looking for an Overdrive myself, but nothing). In fact, all CPUs I've pulled so far are all ok. I'll list them all soon.
I have quite a few Socket 7 Motherboards which need testing, but so far everything has checked out ok. Weirdly enough, I haven't found a single Slot 1 motherboard, but I do have a Slot A - only 1 though and I haven't tested it yet.
The suggestion about making copies of original disks and manuals is good. Most original Floppy disks I've tested so far are barely working. That's to be expected though. I have a few original boxed versions of various software titles (CDs and floppies) which is cool, mainly for the real documentation that comes with them.
As mentioned, I can put up a list of parts here soon. I will respect the fact that selling is not allowed on here, but my list could be of benefit to this community. Please let me know if it's not ok though - I respect that.
Edit: I may also be able to help with drivers and utility software for the community here if needed.