Success! As shown in the pics below, I now have the adjustable clasp on my Speedy 9300 and I can confirm it is very awesome
The parts required were the clasp itself (part 117STZ00154) and two end links (part 118ST1589). All up, the modification cost around $300 USD. Because the new clasp is longer than the original, I had to have two links removed from the bracelet. The first two photos below show the clasp fully retracted. The second two photos show the clasp fully extended. There are five stops in total. The last photo shows the length of the two clasps for comparison.
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