I don't know if this will help your cause but the Spectra has about 989 HP @ 6,000 with 6.5 psi. The strut angle is 7.8* with a 6" drop. The distance between the transom and strut is 25". The cavitation plates are 9.5" from the transom. The distance between the engine and transom is 20". The centerline of the gearbox is 100" from the transom, 4" from the bulkhead and about 15" from the deck/dash. The prop is a 11.75 X 16.5 Menkins 3 blade. Maybe Jim Lange's rule is 1.25" per foot length of boat?