I tend to think Terramite used polished rod for a reason. I just don't know what else is in their rod in terms of alloy, material strength or hardening.
Ford 1920 4x4 (traded in on Kubota). Case 480F TLB w/4 in 1 bucket, 4x4. Gehl CTL60 tracked loader, Kubota L4330 GST
Whatever you decide to do, make two of them while you're at it. If the first replacement eventually breaks, you can use the second replacement while you figure out what to try next.