Installing a Corsair 750 watt power supply should not be a problem. I have a Corsair psu mounted in the bottom rear of my pc case. I have not experienced any problems of any kind.
I took a look at photos of the Temptest. I don't see any problem installing a Corsair psu in the bottom rear of the unit. ATX power supplies pretty much come in standard sizes to fit ATX cases. The high powered psu's may be a little longer from front to back. That is to be expected.