For those that ever have this problem here's a solution: I solved the problem with a lot of head scratching and a whole bunch of luck. That area behind the pulley IS where the key goes. I l positioned the keyway at the 12 o'clock postition and I pulled the top of the pulley as far as I could towards the threaded rod. That gave me just enough room to finesse the key almost into the slot with a pair of needle nosed pliers. it wasn't quite in the key way so I bent some stiff wire and with a few postioning experiments pushed the key into the slot. Could've used a third hand to hold a flashlight for sure. After the key got into the slot I pushed the pulley on as far as I could then tightened the nut as much as possible by hand. I used a lightweight plastic mallet on the pulley to tap it (gently) further and further onto the key.
At that point I was flummoxed as to how to get the nut really tight. Box end wrenches won't fit, crescent wrenches won't fit, and channel locks don't fit either. It finally dawned on me to use a long nosed pair of vice grips. There was enough depth in the throat to go around the threaded rod and the tips were small enough to get to the recessed nut. I had to hold the belt while I tightened the nut little by little but I finally got to the point where I couldn't tighten it any more. I have no idea what the torque value is but I know it's tight. Plugged it in, fired it up, and it purred, well roared, smooth as silk. Typical sound of a planer. Perfect. Put the cover on and sent a video of the working planer to my nephew. He's happy to get a good planer for $20 bucks and change and I'm happy I could fix it for him.
I hope no one else shears the key but if you do the above might help you replace it.
koreywill