Bruce,
I am getting ready to do the same. And after talking to the guys at big jon was told to drill the two tow rope holes inline and 1" lower than the stock holes (I saw another post where someone did 3/4" lower verses the recommended 1"). BJ also gave me some starting fore and aft dimensions for the tow line, which were the standard 9" fore and 14" aft. To get the board to pull harder shorten (trial and error) the aft dimension as it gets the bow of the otter boat pointed more outward.
Jack