you follow the 1.0625 to 1.125" per hard drive spacing specs most manufacturers drill for...
Of course, you will need an 80mm fan at the head of the drives. 3 drives can be cover by on 80mm fan provided it has a thermistor and you put that themistor inbetween the pcb and the drive chassis.
usually they have some kind of non-conductive foam between them now. Make sure you get as close the the middle screw hole and about 1/3 in if possible. that s about where the pan motor "resides"
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BAHHH just scratch that crap you don't need to know.
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BAH just STFU... you guys SUCK.