Turns out I've been running around in circles unnecessarily. The absence of the current sense resistor caused an UCP (Under Current Protection) condition in the MAX1631. So anything I did with that resistor removed would produce the same results. The MAX1631 simply shut down.
I tried bypassing the io's power supply with another unswitched 5v supply with the drive connected, but no memory and not proccessor. The drive started spinning, but very slow. It never came up to speed! I concluded that the problem likely was somewhere else. I finally found that the board was produced with two traces between line one and two of the second USB port. Just the act of soldering pin one caused it to short slightly (enough!) with the adjacent trace. I had removed the wire but hadn't found the short in the process! This happens to be the very same flaw that caused the Apple /// to fail!
Clearing out the short, and rebuilding the power supply returned my +5V supply! Now I reinstalled everything, including the USB mod, but this time I used solder extreamely sparingly and only on the backside of the board. Everything started up properly and I'm back in business.
There is one good side to this blunder. I now know more about the MAX1631 then I ever thought I would have!
Thank you again, Turbo3, for your suggestions. At least I now know the function of the parts within the power supply...