I just opened it up to have a look. A DA-15 connector won't fit without modifying the case, and then there's the issue of fitting the DA-15 to the HDI-45 holes. I suppose the cheapest and easiest solution would be to make a small DA-15 pigtail just hanging out of the case. Someone might curse me for making the mod down the line, but I doubt anyone will miss the HDI-45, and the whole point (IMO) is to have the computers up and running so you can have fun and play with them, not keep them in a bookshelf.

I also powered it up. It bongs, that's a good sign. I gave it a Mac install floppy, but it didn't say which version, probably too old. It made a couple of floppy grunts and then nothing, didn't eject it.