Whew!
The router/gateway machine appears to be fully functional now. Gallery turned out to be a non-problem, since I had installed it from source rather than from a package. The UPS monitor isn't working, but that's because I haven't put the box in the rack yet, so the cable isn't connected. Total time for the nuke-and-repave job was five or six hours; something like three for something that was useable enough to let me get to sleep. Would probably have been about the same if I'd had to restore it from backups rather than the old machine's disk.
Time to declare victory and go home.