As long as it's a 400k disk it will be fine. Formatted on the Mac or XL, it _should_ work either way.
There was an upgrade ROM that let you run an 800k drive in an XL, but chances are low that one is there. If you pop off the front of the Lisa, and there's the newer 800k drive there, then lucky you.
Disks should still be interchangeable between a Mac and an XL.
The XL with Macworks Plus was essentially a big Mac Plus with a 400k drive.
There was an upgrade ROM that let you run an 800k drive in an XL, but chances are low that one is there. If you pop off the front of the Lisa, and there's the newer 800k drive there, then lucky you.
Disks should still be interchangeable between a Mac and an XL.The XL with Macworks Plus was essentially a big Mac Plus with a 400k drive.