Yes it is possible to reuse the Apple fans. Unfortunately the Apple fans are fairly noisy and use much more power then selected fans currently available. Google for the wiring.
Know your motherboard case fan support circuit and logic and select fans accordingly. Or if you are biased toward 12V fans powered directly from the PSU, select carefully as noise, air pressure and flow are not a given.
And the Mac Pro rear fan is 120 mm.
neil