I have two 9.5’s, both with the same problem, the reverse lock mechanisms are missing parts. One engine has only the #30 latch and spring, the other has a latch, spring, and a ratty cable that goes to nowhere.
I understand that this was an "automatic" system- it was locked only when you were in reverse, and became "released" when in neutral and forward. The parts explosion is unclear on how this connects, does anybody know?
Look under the hood, at the levers that the shifter handle moves. See the round interlock pin, combined with a hex screw? Held by that screw is a thin lever, which moves up and down when you shift. Through the end of that lever goes a thin rod, which extends through the swivel and comes out at the "claw" that hooks onto the tilt rod when in reverse. The rod attaches to a barrel/setscrew assembly that is adjusted to it locks in reverse only.
Busted motor mounts fouls the whole thing up, but it sounds like you have something else going on.
You say thin rod, but I think it’s a piece of braided cable. Maybe one end is factory formed to engage the upper lever? The lower clamp looks to be a barrel like they use inside a remote control box to attach a cable core to a sliding rack for throttle or shift.
I suppose it could be a cable, but that is it. It’s been a long time since I worked on one, but I worked on a bunch of them back in the day. I remember it as a rod/wire with a "head" on the upper end. Feeds down through the upper lever to the barrel thing.
The one that still has the cable, it’s nailed to the lower shroud, permanently unlocked. They sure got fancy down there. Lots of rods, locks, levers, ratchets.