I dont have personal experience with the Tru380, but from past experience with a dual fan PSU, it was one loud mutha.. I had great performance from my PP403X in a dual Tiger MP board. I highly recommend it.
You CAN change the cpu and hsf while mounted, and I have a number of times, but with the delicate Athlon core I recommend removing the board to mount for safety. A cracked core can be very sad indeed and if you dont seat the hsf well you will be having loads of problems if not now, later. IMHO