My AC Mack had four slots in the valve plugs. I never saw a tool made for that. I made one out of a Lincoln rear caliper piston that had an 1 1/8 hex in the center. The OD of the plug was 3 3/4 inch. A number of the old jug type engines had valve plugs because they didn’t have removable heads. Bulldogs had 1 7/8 valve heads , but yours was probably for a normal size auto engine valve plug. When the spark plug was at the bottom of the plug, you could thread a plug in the spark plug hole that was drilled and tapped for a bolt and washer to hold the tool down onto the valve plug. Hmmmm, an awful lot of the word plug. I hope it is not too confusing.