The easiest thing would be to boot the Alto off a good disk, then swap the disks and write a good boot environment to the bad disk. (You can switch disks while the system is running.)

One of the guys working on the restoration (Carl) is building a FPGA-based disk emulator, which we could use to re-write the bad disk (as well as read and archive disks).

The Alto supports network boot over Ethernet; I'm working on a BeagleBone-based Ethernet emulator/gateway so that's another option. (The Alto's 3 Mbit Ethernet isn't compatible with anything modern, so I can't just plug an Ethernet cable into it.)

> You can switch disks while the system is running

Is that something you can do at any time, or only at the "home" screen when no apps are running?

I think you can switch disks pretty much any time. The Alto doesn't swap to disk so the disk is only being used when you're loading a program or loading/saving a file. As far as how it's used, think of the Alto's disk more like a floppy drive than a hard drive. (Although since it takes a minute for the disk to spin up to speed, you don't want to switch disks too often.)