Remixed the long version remix to make it even longer so I could use the 2 holes at the back to attach a 120mm fan. I mounted the brackets backwards of the original to make use of the two extra holes.

It should be compatible with the long version to stack but I cant guarantee it as I designed it from scratch in Fusion 360. STL files are too much of a pain to try and modify.

The fan bracket should fit a standard 120mm fan with standard fan mount screws. The bracket I used a M3 nut and bolt. Its a bit loose but I was using the original hole size. Once its screwed tight its solid. I originally planned to use both holes on the top and bottom but its probably not really needed.

Same bracket is used for top and bottom, just attach it upside down on the bottom.

The 120mm fan is a bit larger then 4 drives stacked so I'm not sure you can stack 8 with 2 fans. You may need a spacer drive between. I don't have enough drives to test.

I included the fusion files so its easy to remix. Sorry the bracket is a bit of a mess, it was a lot of fiddling and adjusting.

Tip: if the nuts are too tight, press them in slowly with the tip of a soldering iron on low. They then melt right in and make a nice permanent fit.