Annoying feature of the aluminium enclosure. The aperture just isn’t large enough, for some drives.
There is probably a clip-on plastic bit on the front of the tray. Hopefully, this should come off, and then the drive tray will be able to pass freely through the aperture.
I tried a Lite-On drive once, in my Mac Pro (similar case), and found the tray was 1mm to low, to clear the aperture edge. Very annoying. The Panasonic drive I replaced it with, was fine, after I’d removed the plastic tray front.
The G5/Mac Pro drive bay door is designed to work with drives with the clip on tray front removed. but it is a design flaw, I have to say.
HTH.