Sorry, Wardie, that swap is not on. The 60 Sport is a bored-out 50Sport, and the 50 Sport engine castings are all around 20% smaller in dimension that the 90 motor. The 90 cylinder spigot is too big to fit the hole in the 60 crankcase, and the 90 Sport gudgeon pin is too large to fir in the 60 con rod.
Graham