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[Bushwacker]

Big outboards didn't always have power trim! Any older motor without power trim should have a specially made pin just like you're looking for. My 1975 115 Evinrude had one with a pivoting locking tab on one end with a spring and 90 degree bend on other end. You'd just rotate the bent end to point up, push in and the tab would unlock so you could pull the pin, move to another hole and rotate bent end down and push in against spring to lock in place.

The pin only limited how far the motor would drop down. I don't remember it having a feature to lock the motor down, but it did have a lever on side of bracket you could move before you tilted motor up that would hold motor up after you manually tilted it. You had to move the lever down to tilt motor back down and that may have automatically locked it down.

I had a 1966 100 hp Evinrude with a similar pin that had a lever to engage the locking feature to prevent motor from popping up in reverse but I never used it. The motor was heavy enough and I never used reverse hard enough to need the locking feature.