Hi Keith. I am sorry that you have received no replies so far. I have a 71C with flanged output, and a parts diagram for it, but it does not show a splined output, so I cannot be of direct help to you. A few thoughts come to mind, however.
First, re-post your question on the Motor Boat Forum, where it is more likely to be read by somebody with the answer.
Second, contact Lancing Marine (Marine engine gearbox sterngear Ford Lehman PRM ZF ), because they used to sell Sternpowr with Velvet Drive gearboxes, and may be able to clarify matters, as well as sell you the missing bits.
Third, I suspect the numbers you have identified are model numbers for the different gearboxes. That raises the question as to whether the only difference between them is the output shaft and tail end casting. If so, it should be pretty easy to swap the relevant parts from one to the other, subject of course to cleaning up the old casting should it have suffered from the water ingress, and replacing bearings and gears within the assembly as necessary.
