The 3k version is tight with no modifications, I have never installed a 4000 version in a 3000 but I would bet it would be an effort even beyond hacking the tray...
Importantly, I think only the 3k version had the CIA jumper wire so you can use the fast scsi II controller on board. The SCSI controller is really nice I remember it being really fast...
The 3000 version maxed out at 64mb ram, where the 4000 version maxed at 128 mb.
I installed this well over 10 years ago, so I'm fuzzy on the details...