Heh. I just measured mine AGAIN - and it reads 1-1/2"
I have others but its too far to walk to the top of the barn to see.
Some have said to substitute a V8 ratchet nut in this location "because it's stronger." May I have one of those on this engine?
As you say - there is probably a deep socket or a wrench made in whatever size it may be - even metric (Gaz engine?)
Somebody out there in Model A supply land sells a device which bolts in place of the starter motor - and gives a small crank which can be turned to precisely locate the motor for timing. But I haven't seen this for a while.
Joe K