Shaft length for Caribe C-10x

[AST]

Hi
I was given an old rib caribe c-10x. Previous owner knows nothing. Looking at caribe website it says I should put short shaft 15". I measured the distance from the top of the transom to the bottom and it is 17". Bass pro thinks I should put Ling shaft 20). I measured the distance on a short shaft engine between the rest bar to the cavitation plate and ot is 17" (not 15). I always thought that the cavitation plate should be at the same level as the bottom of the transom. If that is true then yeh it should be short shaft. Any idea?

[GreenWave]

I have one and use a standard 15" shaft Yamaha 9.9.