Fine. Here is that tutorial I talked about, describing and showing how to remove top floor.
All what you will need is:
Crossed screwdriver, normal size, nothing special
Torx screwdriver, size no. 8 (for those Apple screws)
Small imbus (imbus = socket head) wrench
G5 case

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What do we have here? Torx and crossed screwdrivers in that case

Remove screw catching those chassis fans

We have to remove locking mechanism including that ledge to remove top floor. First, remove these small black flexible metal laminas, use just nail on finger. Remove all three along the ledge



Fine. Take imbus (socket head) wrench and unscrew these screws holding sliding ledge

Unscrewed one

Put out all three doorlocks

One is out, two left

Now we have to remove small metal circle holding axis of ledge on lever.

Use knife with sharp spike. But be careful, dont lose that circle, you will need it back then.

Removed!


Remove axis, dont lose transparent underlays.

Fine, all gone. Now we will move out that ledge.

Put it to this position to put it out. Normally you cant do that beucase it is hold by lever.

Out!


Now unscrew the rest of torx screws holding top floor.

Ah, forgot for cables. Remove them from plastic "shaper"

Time to unscrew rest of screws...


Floor locks in opened position, close them.

Closed!

Now put floor by hand down. It will not go smoothly, but it will go.

Just a little bit. Now catch it and pull it up, just like on next pic.

Pull it up to get holes out of bases for screws. Pull it up above that bases and then pull to right, in direction of hole for optical drive tray.

Bases in zoom.

As you can see, you can't put it out smoothly beucase of no space on other side... You have to
a.) pull it to left as much as you can
b.) bend a little bit backside with PCI cards holes to make space for top floor to remove

Finally, it is out. Just pull it up out of case

And thats it!

Result, without top floor. Now is easy to remove hdd tray and those fans, if needed.