Ghostrider,
In my collection of OD transmissions and regular 3 speeds, some have the small shaft like the one on your OD and some have a solid shaft like the earlier AD trans in your picture. I'm not sure why there is a difference but both will work equally well. I have probably rebuilt 50 of these transmissions and have never seen anyone break the clutch gear. This basic transmission was the standard bearer for the early Corvette (with a 2:20 first gear and steel syncro rings) before the 4 speed became popular. Pontiac also used it 57-58 with a bigger set of gears. They hold up ok if you understand their limitations. Fred