Hi GUY'S,
A bit late on this subject but here is how I make DOG & BONE couplings.
Get a flat used file about 1" wide by 3/16" thk stick about 12" into a coal fire and leave it there until cool in the morning.
Cut off about 5" of the file with hack saw
Drill and form a a hole as shown in pic to suit the size of the ball, hole to be . 015'" dia smaller than the finished ball to allow filing to final dia, make sure that the cut is 7deg to allow swarf clearance.
When completed re harden the tool for cutting the ball.
The driver to the engine is a simple turning job and the final ball has a 1/16" dia rod drilled thro'.
When finished case harden the mild steel components.
All done quite easily
George.