Thanks for the very useful advice. Unfortunately, the suggestions will probably not work for my specific situation (except for the EMU disk emulator).
Maybe my experience will be educational for others.
First, I am original owner of a Macintosh XL (I assumed it was new old stock), which I purchased from Sun Remarketing in 1991. It has the screen modification with the 3A88 ROM, so original Lisa disks will not work. I tried to read a 400k disk I made with Disk Copy 4.2 of a Lisa image I downloaded from Bit Savers. The Macintosh XL could read the disk, but the screen was a mess; I assume the screen was just a set of horizontal black lines because of the 3A88 ROM.
Second, I lost the original keyboard, and I am using the keyboard adapter with an Arduino, which I discussed in a different thread.
Following the instructions from the Sun Remarketing-published “Do-it-yourself guide,” I tried to enter service mode by pressing “any key” after the first click, but nothing happened. With the original keyboard in 1991, I had been able to use the service mode, but I wonder if the Arduino program emulation of the Lisa keyboard does not work until later in the boot up process.
Since I have the original 400k disks I made in 1991, I can use the programs I bought the computer to run in 1991, so I am relatively happy.
My goal over the weekend was to use software from Macintosh software websites that I use on my Mini vMac emulator and my Basilisk II emulator. One issue is that a .dsk disk image is not compatible with Disk Copy 4.2, and I cannot find a way to convert a .dsk image back into a Disk Copy 4.2 image.
I assume that the .dsk image can be read with the EMU disk emulator, so maybe I will buy one someday. Again, thanks for the helpful advice.