I think the question got pretty well answered before the confusulation began.
1. Bracket for metal-hood Johnsons had the prong for the hood mount.
2. Earliest ones (15hp) had the small 6 Volt starters with different thru-bolt spacing than the 12 Volt version
3. At some point early-on, a prong was added to guide the spark plug wires.
4. When the silencer was eliminated, there was no need for the support for it.
?? Didn’t the solenoid mount on the opposite side when the junction box was eliminated??
Sorry, I don’t have the specific years’ information right at hand.
And I may have missed something. And of course I may be mistaken.