[packrat79]

I should have figured there was an easy solution... my lack of experience must be obvious. I hadn't tried heat on this bolt yet, so I tried heating it with a simple propane torch. The first attempt didn't work, but on the second attempt the bolt finally gave way and I was able to wind it completely out. I'm glad I got it off without damaging anything else - there's already enough wrong with this old heap!
Thanks for the advice.... I'm sure it won't be the last I'll be needing.