lower unit exchange

[eric the fisherman]

i have a 1989 looper v4 vro 120 hp with 4.25 gearcase 13 spline prop shaft. the top secrect file said these engine have a 4.75 15 spline prop shaft but mine is 13 spline. i need a 4.25 gearcase with 13 spline looper lu of a v4. any suggestions on hp models and compatable year engines for this gear case and lower unit.does it have to be a looper engine.the big gearcases where off industrial engines .please help need to be fishing thanks