Right on Briggs Clutch tool. I have one, I've had it 54 years and have not had a new Briggs engine in last 15 years so I don't know if it fits still. Have not used a push mower in 25 years or so since I have a large steep yard and have used Gravely walking mowers until last year when I bought a Gravely zero turn.
That makes sense since he was into repairing small engines as a hobby after he retired.
I hear you on the Gravely, I got tired of pushing a lawn mower at my grandmother-in-law's place every week...took my c10a over and mowed several years with that.
I still have 3 gravely's left. Oldest one is a 1952 L model 7.6. I rebuilt it 45 years or so ago and used it up until 5 years ago and knee surgery. I used it mostly for earth moving with a snow blade and an earthcovater blade I adapted to it (sort of a lanscaping box that rotates to push or pull) and rotary plow and tiller to break the ground up. I then bought a belt drive 48 inch gear transmission mower that I rebuilt and used about 10 years, then bought a new hydro 48" walkbehind that I used 13 years and traded in on my new 48" zero turn. I also have a 85?? series Kohler motor new style mount that I have used as a bush hog around the house. My Bobcat T200 does most of my dirt work and heavy moving so Gravely's mainly sit, except the zeroturn.
I have two working Gravely, a c10a walk behind and a 8162 rider. Multiple attachments for each, plows, snowblowers, rototillers, mowers, rotary plow, sickle bar, etc.). We have a Model D in the family and a 60s something C8 that my father still uses (along with his 8199kt progessional).
I have too much yard for a rider, bought a use Grasshopper for that chore.