I can’t remember if my 430 from 87 has the other hole or not. Though I do know that the bolt has a lock washer on it, and when the flange was broken, it backed pretty far off the threads.UPDATE: After looking over the Service manual, I see what they did and why. Funny thing is, the brace has both holes (one slotted) and I do have a shoulder bolt that until now I had no idea what it was for. And it fits. I guess perhaps the rear end was serviced at some time and they installed the update which may explain it. The manual only states "in later models". No SN cutoff.
I'm sure glad I caught that thanks to you. But now I'm questioning the model year. So far, everything else matched but I'm not that far along.