Hadn't really intended to pull it apart and check things, but with that level of enthusiasm how can I not? 😁
1. POD @ 83Mhz - If memory serves it helps Quake run playably. Pretty much everything you'd want to run on this machine will run with any higher-end 486 chip, and most will run fine with a DX2/66, but I love esoteric stuff and maxing out machines with strict limitations (like this one). I think pretty much everything else that I threw at it either ran fine without the floating point boost of the POD or else wouldn't run even with it. However, I suppose if you were feeling particularly psychotic you could try to install XP with a POD in there.. 😜
2. No damn clue, really. I tested dozens of SIMMs at one point and labeled them with their capacity if they weren't already, so I just found two with 8MB that the machine was happy with. One is marked, so you could hunt that down, but the other is not.
3. Mostly I network transferred things. I set up an FTP server under DOS and FTP'd things over to it from my modern machine, and at one point I shared on WFW3.11 and accessed the shares on a modern box. That said, no reason you can't hook up parallel port SCSI (which I have, just need a terminator to get here in the mail so I can hook up an optical drive). I also own a lot of weird media like ZIP100 and LS-120 stuff with external parallel port drives so I can use that too for transfer. Worth noting that nothing *needs* a CD-ROM really if you're willing to crack it, but you will lose out on CD audio on certain titles. I played through a pirated copy of the DIG on this box with no CD-ROM drive and it was great.
4. I have not. At one point I also had the spec sheet for the chipset that I'd hunted down, not sure where that got to though (was a PDF) - should still have it, but my HDDs are terribly unorganized. The manual covers some interesting things (diagnostic codes, etc.) but doesn't detail potential memory for the system - which is odd, I'd expect it to at least mention the requirements but nope. It's the "Maintenance & Service Guide", by the way.
The HDD I have in there is 120GB - I probably switched to that because I suspected that while it reported fine, the 750GB disk may have been not actually fully usable - that or I just wanted to use it in my 300Mhz Pentium box (where it currently resides).
Pictures of RAM, insides, CPU, and outside: http://imgur.com/a/p5OSU