The display part of the 4-line displays is 1/4" shorter than a single 1/2-height drive bay. In theory, it could fit, but it would be a very, very tough design.

Can you try testing the unit with a different piece of software? Yes.

I tried LCDC, and it worked OK for the first few lines, but then things began to screw up just like above. It looks to be heat-related in the VFD, since it seems to work OK for a while if I plug it in after it hasn't been used ...

Can you still communicate to the display? Yes and no. Although LCD Tester can talk to it enough to get information about it (capabilities, etc.), and some things seem to work, I can't tell if it is accurate. What types of weird behaviour was the unit exhibiting before you powered it off? At first ...

I just received my VK204-24-USB and was playing around with it using "LCD Tester" (Windows). After a while, it seemed to be doing some weird things, so I powered off my machine and turned it back on to see if that would clear the problem. It obviously didn't, because the startup screen ended up ...