15hp Johnson short shaft

We have a 15hp Johnson that needs to be converted from a long to a short shaft. I am under the impression that the short will just bolt on once we take the long off. Anyone have a short or know where we could get one? How much do they usually run? Thanks for the look. Any info is appreciated.

Honestly I have no idea. I know the Johnson is early 2000s. I will check. What year is the Evenrude?

I'm not sure on the rude but I think late 80's/early 90's.  Might be too much of an age difference.  
 
I have no clue on the internals of the rude lower.  I received it as a "parts" motor when I bought my boat in '08.  The rude's powerhead is bad but was told everything else should be fine.  My boat has an '84 15 hp Johnson on it.  I have used some small things off of the rude but not a lot.  
 
If I get the chance tonight, I'll get the serial number off of it and look up the year.
 
 

Off by a decade.  It is a 1978, Model No. 10824M.
 
Have no idea if the lower unit is compatible.