Re: Dumb question about 1988 Force 50 HP outboard...
The only way we as boaters have to check for a spun hub is to run the engine on the water and see if the prop slips. So what I am saying is: Don't assume that the hub is bad. Just because it is old does not automatically mean the hub is spun. Why buy a new prop if it is not necessary? And re-hubbing the prop should only take a week and cost around 40, maybe less in that size. So, run the boat early in the season just for shake-down and see if the prop slips. THEN repair it if necessary.
Now, if you want a spare prop, Why drop 130 when you can get a good used one for much less on ebay? Matter of fact, I have a new one that I acquired and I might be willing to part with if I can find its very safe storage place. PM me for details. See--when I open my garage doors, stuff spews forth like vomit. And by stuff I mean Sugar, Honey, Iced Tea ---Courtesy of childs film "Madagascar."
Anyway, there are only about three pitch sizes for that 10 3/8 prop. 11 1/2, 12 1/2, 13 1/2. First is for heavy loads, second is for average conditions and third is for light loads. So you need to decide where your boat falls.
As for a member of the board? I sometimes re-hub my own props but by the time I buy a hub then you ship the prop to me and I ship back, then I get a little for labor---The prop shop picks up from the marina and delivers, and the hub costs the same so you are way better off both in time and money having it done locally.