Got busy with my AT some more. I decided to try changing jumpers around on my controller card and lucked out, after the second jumper that I pulled I could now access the 20MB MiniScribe drives. One of them had an intact DOS partition and I was able to recover a bunch of files from 1991 (looks like school work). I got a new (to me) EPROM eraser in the mail, zapped some 27256s and then programmed them with the AMI 286 BIOS from minuszerodegrees. I also popped in an 8-bit Video7 VEGA VGA card and ran the benchmark on it. It only got about 850KB/sec, similar to the 8-bit bus memory board. Here is a (short but big: 120MB) video of the computer booting: http://www.hyakushiki.net/junk/turnon.avi
Since I have the newer BIOS, I can use a regular ISA IDE controller instead of ST-506, although there is a 1024 cylinder limit. I hooked up a WD Caviar 2635F which I was pleased to see is still working. This was the main HDD in my PC until like 2002, when I finally replaced a pair of old WDs with a pair of Quantum Fireballs.
I went hunting on my other PCs for some old software to run. I tried a couple of games: Megaman 3 and Overkill. They're a little slow on a 6MHz 286, probably need something more like 10-12MHz. I loaded a couple of photos with Compushow 2000! (takes quite some time) and discovered that the VEGA VGA card has an 800x600x4bpp 49Hz interlaced mode. The Paradise VGA card also supports this mode, as well as 640x400x8bpp which is a nice bonus on top of standard VGA modes. I found that Win3.1 could start in standard mode with only 64KB of free XMS.
A funny thing happened in not-so-retro land. I tried to run a graphical DOS FreeBASIC program inside an OS/2 DOS session that was running in Virtual PC 2004 on Windows 2000. And the computer spontaneously rebooted.