Thanks everyone! My hacked screwdriver worked OK, but I'm planning to fashion something a little better this weekend.
I got a bit distracted when I was making some adjustments and my knee bound up and wouldn't move down at all... It went up reluctantly, but not down more than 1/2" without jamming.
I thought there might be some chips jammed in there, so I loosened the clamps that hold the knee to the column and it still wouldn't budge.
One thing lead to another and I ended up taking off the table and cross slide to see what was happening.
Wasn't until I pulled the knee adjustment shaft that I discovered that the jam nut behind the handwheel had come loose and it was spinning with the handwheel and jamming everything up.
While it was all apart, I took the opportunity to scotchbrite a bunch of rust off of the ways and cleaned out 50 years worth of chips and dried grease.
She's all back together, lubed up and ready for another 50 years of service.