75GSX and 59GSX are two different families of drive. Maybe the heads are cross compatible, but I highly doubt it. I guess you never know unless you try it.
Not necessarily. There are other things to look for such as label on heads and slider topography. For me this would be a last resort. This would be a good example of the need to experiment first on a drive other than the patient. But then you'd have your matching donor
As Jared said, they're different families and it's best to "keep it in the family".