The bass boat was made by {AMT I think, but possibly Revell} and was included (along with a trailer) in a pickup truck kit. They also did a jet ski/trailer/pickup kit.
That would have made it the typical automotive scale of 1:24 or 1:25. This is not to be confused with the 3-in-1 custom race boat -- also by AMT.
I suggest you go over to the automotive chat & ask about it there. Someone may have a better line on it