This Floppy Drive is fitted in my System 4, its in a 42HP wide, 160mm deep, 3U high module (Verotec 957-236391). The drives are attached to a pair of fabricated aluminium U-channels attached to the inside of the left and right of the module guide rails. The internal dimensions of the U channel are 102mm high and 19mm deep (the front to back dimension is not critical 100mm). I didn't use the standard module rear panel but fabricated my own (I didn't actually buy the full module but made this mainly from parts I just had to buy the 42HP front panel (Verotec 957-235360)).
Side View (right side)
Top View
Rear View