Don't know. I've met one other person with one, and his was a B I. He was not the original owner, but thought it was all original. Could have been an engine swap. The manual says very little about them, just a small amount of info in the Tech manauls.

Edit: Went back and looked at a Powerboat article from August 1993 on the 257 Legend. It says the PT engine is a combo with the B III, not available otherwise. So obviously a swap out above.