I recently found a Nintendo N64 at a garage sale for $5 with MK4, but no controllers, and the power cord had been chewed off by a dog or something. Knowing it was probably fine, I bought it and went about replacing the cable. Of course the gamebit I had was the 3.8mm variety (for opening games, not consoles), so I had to needle-nose it out. Once that was done, and it was open (there are some clips on the other side of the power supply opposite the screws), I couldn’t get the PCB out. After looking and looking, I just wrestled it out with some force, and found that Nintendo, for some reason, used some double stick foam tape to secure the top of the transformer to the underside of the top of the casing.
So… in short, once you have the screws out and the case apart, you’ll just need to yank the thing out of the casing.
And yes, after replacing the cord, I was able to fire the unit up just fine. Yay for cheap gear!