Matt,
Had a look in the shed and found the propeller shaft which had been removed from my Police Launch. I've overlaid in on the plan. The length of mine was a 7" outer tube, which is shorter than the original plan, or the 8" suggested on the instructions provided with your kit. The reason for the shorter shaft was to allow for the length of the huco coupling and ECO 600 motor. This installation still retained the correct tube length under the hull.
Looking at the original plan, the shaft length is approx 7.75" long which appears to be a unit manufactured for the 1 cc E.D. BEE Diesel, which would have been the power unit many years ago. This appears to be a close-coupled unit, without having seen one I can only guess no flexible joint was part of this early installation.
The propeller in the photograph isn't the correct one ( It's obviously too big just happened to be one I had in the spares box), screwed on for this illustration. It may be worth laying out your chosen coupling, motor and propeller before choosing and ordering the shaft.
