Gas EZGO 1987? marathon rear differential spline and pulley

[buggynovice12]

Does anyone know what I would need to put a pulley onto the spline that is coming out of the rear differential on the late 80's EZGO marathon? The differential or transaxle unit has the spline pointed toward the front of the cart and I have a pulley (torque converter I think is what it is called) for it from a different axle. I am mounting a 399 rotax engine that hasn't been used in 40 years and I just got it running last week! Exciting day for me to see that engine purring like new! The engine has the front pulley that squeezes the belt and the rear pulley expands for the belt to fall in to. I am wondering how to mount the rear pulley onto the spine of the 2 stroke 1987 EZGO marathon transaxle.

I don't think the pulley will just slide right onto that spline. Is there a way to do this with some kind of spline adapter?

Any help and pictures are appreciated! I'm new to this so I apologize if my questions are too simple.

Mike