Re: not enough splines on hub
Look: I don't know the prop numbers. Given the information that you first gave me it appears that you need more research. That's what probably, maybe, but not likely meant.
If you have the HMS catalog and can measure the inside diameter of the prop hub itself and it matches the outside diameter of the rubber hub, then yes, it would be reasonable to think that someone has already re-hubbed the prop to other than Volvo and yes, you should be able to go back to 19 splines. By matches, I mean the prop is the correct size to properly compress the rubber hub when installed.
IF you have a prop shop close by and can talk with them, then you may get a quick answer. However, sending the prop out without discussing exactly what you need is a recipe for disappointment. Make haste slowly.