I am restoring a Merc KE 4 . Went on this site to learn how others were removing water pump cover. (I destroyed my Mark 20H plate and had to replace it.).
As was looking in my tool drawers, I ran across this spanner wrench I’d found at a garage sale. It is made by Wright Tools (tool number 9636). I tried it and it worked. I had to tap the end of the tool with a peen hammer and used Kroil penetrant, but plate released fairly easily. Don’t think it has ever been removed previously. I’m adding a photo. Tool might be available at White Cap stores or ordered from them.
it’s adjustable and pins fit perfectly and just long enough. Mine is a 2” version.
hope this helps
Steve