Magnum motor with Mechanical fuel pump ?
I have one of these adapters on my Magnum 360.
My brother has had one in use for ten years or more now on his Magnum 360 with a lot of street miles and run time and no failures.
The key is basically only for initial alignment of the cam gear. Stock keys and adapter keys usually fail because somebody did not tighten the bolt properly or used a lower quality replacement bolt.
The fit of the stock style key into aftermarket camshafts is occasionally way too tight also. Consider the key the cheapest part to modify. File it until it can be tapped into the camshaft without excessive force, then file the other side to just snuggly fit the camshaft sprocket itself.
Once everything fits properly, use a drop of red loctite on the threads of the camshaft during final installation.