I decided to have the blades and stump jumper modified to accept a common brush cutter bolt I could get at TSC. I had the machine shop enlarge both holes and cut a key slot into the stump jumper and use a bolt that had a key in it. I picked it up yesterday and ran it a little, it’s much better this way. The blade swings freely but the bolt is locked into the stump jumper by the key and being torqued down to 300 ft/lbs or so with a lock washer. I think I’ll probably break something else before the bolt fails again.
I never did get any response from the manufacturer (JCT) and I’m seeing a whole lot of their brand new equipment at the Ritchie Bros auctions lately so I’m wondering if they’ve gone out of business. I guess I’m on my own for any repair parts so I’m glad I made the change, even though it was a bit more expensive than I’d have liked.