Hi I’m from South Australia I have an 1961 s series that needs tlc

I don't know what an S series transmission is, BUT, you will need to pay close attention to the crankshaft register where the flywheel seats. The early engines (up to 67 I believe), used a smaller size register than the later (68 and up), so you will need the appropriate flywheel with the larger center hole. At least that's how they did it HERE.