Sorry if I hurt your fillings.
But the answer really is in the way the two guns work.
A SA hand is mounted on the hammer, and it and the cylinder ratchet are more closely comparable to a bumper-jack then to the S&W hand & ratchet.
With the SA, once the bolt drops in and locks the cylinder, you can't pull the hammer back any further, period.
The hammer is supposed to contact the grip back-strap and stop, but if it doesn't, the hand is built like a tank, and it won't be damaged.
The S&W hand is mounted on the trigger, not the hammer, and is much thinner & much more delicate then a SA hand.
It depends as much on the width of the hand as the length when setting the timing, as it must slip off at exactly the right time or it will be damaged, or the cylinder will lock up either in SA, or else in DA, or maybe both.
It's really hard to explain in a post, but it really is because one is a SA, and the other is a SA/DA.
Since the SA/DA's hand & ratchet operates differently, they just require more precise & delicate fitting to work right in both SA and DA operation, especially on the older S&W's.
I think the new ones with the CNC'd frames, cranes, and ratchets, and MIM hands & bolts probably come much closer to having interchangable cylinders then the older hand-fit S&W's.
But I don't know for sure if that is true or not.
rcmodel