It is a beast of a case for sure.
I looked up the Flux Pro, the wood accents look cool. Nice looking case.
I took a closer look at the drive bays and it looks like not only are there screws but rivets. It shouldn't cause too much more work, but I'll have to drill them out. I'm debating if I should remove the motherboard before I do this, but I think I can get a way with taping some cloth over it. The risk of debris causing an issue is likely low, but just to be safe.
If you have a spare pair of hands, run a shop vac next to the rivet while you're drilling it. Should suck any debris away, in theory at least.
Ended up coming together nicely. Losing the DVD drive for now. I'm going to have to cut the bay in half to remount it. It's probably been about a couple years since I've used it anyways. I might not bother.

Looks good dude! What kind of fans do you have up front? If I recall, didn't that thing have something like a 360mm fan for intake?
You're going to some lengths to keep that old case going. Is that THREE HDDs in there? I'd offload that to a NAS and tuck it in a closet. I wouldn't be able to deal with that noise from those things.
Excellent idea.