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.
“Nine-tenths of tactics are certain, and taught in books: but the irrational tenth is like the kingfisher flashing across the pool, and that is the test of generals. It can only be ensured by instinct, sharpened by thought practicing the stroke so often that at the crisis it is as natural as a reflex.” ~ T. E. Lawrence