Good day Ribeye 330
Most engine manufacturer use the same block (same displacement) for different horsepower. Your MARINER (made by Yamaha before 1980 and then by Mercury) was probably available in a 50hp and 60hp version, therefore the “50hp with a 60hp block”. Even today the 50hp and 60hp from Mercury have the same 4 cylinder 995cc engine block.
A lot can be made with “elbow grease” especially if, like me, you have (almost) as much fun working on your boat than using it. You will be able to give a much better look to the complete rig. If everything related to the console is working well. I suggest using it at least a season before replacing it. The choice of what to install and if the remaining value of the boat justify it will be more clear. Because, even if “Be aware you will almost certainly be financially better off taking that boat to the scrapyard and buying a better condition one” is a very crude way to say it, it is easy to spend too much on a boat…
Have fun with your Searider !