I also had issues when trying to use my 18TB WD which was shucked. I didn't worry about trying to get all those screws in from the bottom, not that I'm sure I could have if I tried.
My problems were:
1. The large HDD wouldn't actually snugly into the bay, I really had to force it as the plastic on the tray bent. Unfortunately though, the bending only helped line up the screw on one side I believe. (I did this a few months ago so my memory might not be 100%)
2. The other big annoying issue was sliding the tray into the bay. First I tried sliding it into the two-slot bay as I thought that bay would be healthier for the drive regarding vibration. It physically cannot fit into the top slot. It'll just fit into the bottom slot, but getting it out back out was extremely difficult. I had to stick a screwdriver in there or something and use it as leverage to push the back down and slide it out, even doing that with multiple tools and being a little scared that I may damage the HDD, it nearly didn't work and I got it out by less than a hair. The key spot to put one of those fat drives is in the middle of the three-slot bay. If you don't have many HDDs at all, you could also possibly test it on the back slot.