I have been real uncomfortable with the idea of heating the cast iron. With no experience I don't know how much it can take before warping. With my thinking cap on, I thought of another idea.
This afternoon, I tack-welded a sturdy piece of rebar to the bolt head. The rebar was like a wrench handle and lo and behold, the bolt loosened! I twisted the rebar off and finished removing the bolt with vice-grips.
Then, the fun began. I've spent this evening dismantling the spindle assembly. Pictured is what was in the bottom of the spindle case....the remains of a bearing! The outer race is intact. I believe the broken metal is the remains of the inner race. The spindle shaft and bottom bevel gear are both torn up where they touched the bearing.