A little more difficult than I first thought.
I had my Mac Pro 1,1 diagnosed by the Apple Genius bar at our local mall (Beavercreek, OH) as having a burnt-out PSU. The instructions supplied by ifixit were spot-on as usual, and at first glance I thought such a repair would not be too bad. The difficult part for me were not-so-slender fingers.
I had difficulty removing the connectors by hand because I could not get a good grip on them, eventually using angled needle nose pliers to pinch the clip on the connector so I could disconnect the connector. The hard part was putting back the connectors for the refurbed power supply and making them line-up so they could be re-inserted. I borrowed my wife's much smaller hand and fingers and she reconnected the connectors in about ten minutes or so. Putting the PSU back into position so it could be screwed back into the frame also required a little thought as the initial placement proved to be off by about a quarter inch.
Aligning the ribbon cable so it would bi-fold beneath the power supply allowed it to seat parallel to where it needed to go, and gently shoving the PSU back so it seated firmly against the back of its space allowed the four 2mm hex screws to line with their holes. I found an old fashioned allen wrench worked best rather than one of my t-drivers, they were too long by about an inch to get into position to remove these screws.