It's out! The more I tried, the more determined I became to save the lever. I know it was ridiculous and I know I should have dremeled it off and been done with it. Stupid is as stubborn does.
I could bore people to death with every detail of every (many) attempt but that would not result in a concrete explanation as to why the gunsmiths hex key finally broke it loose.
Heat was applied. t6 torx wrenches were mangled. allen bits bit the dust. I even ordered a WERA driver. I'm still waiting on delivery, but...
Thinkig WTH...I took the lower with me on an errand to the LGS and told the smith what I had attempted. He said let me see that thing, disappeared downstairs for a few minutes and returned with the right side safety in one hand and the set screw, wrench and lower in the other. He said it was tight but twisted until it broke loose.
The tip of the wrench' short arm is twisted a little. I have it. He gave it to me. Every one I had tried wound up much more mutilated.
Did the repeated heatings have a cumulative effect? Maybe. I left the pic huge so that you could judge for yourself.
SCROLL RIGHT to see the screw and thread lock remains.