jhenry, congrats on finding a fine old Heavy Duty. I had the chance to play with one quite a bit when I was about 20, although that one was a five inch. Your experience with loads and such mimics mine. By current standards, anything under $400 is a good price for one in good condition.
I'm inclined to think if a man hasn't gotten his point across in 4912 attempts, 4913 probably isn't going to do it.