walker with the 750 Kubota engine

I have a 24.5 hp Walker mower with a liquid cooled Kubota engine. looking to replace the engine with the 752 Kubota, but I am told you have to take a bunch of the new parts off and replace them with the parts off the old engine the 750.... like the starter alternator etc. I would like to know why. anybody? The other option is to rebuild but a short block is not available. what about the other parts?

Walker have an excellent customer service department I have delt with them on several occasions.
Tell what you want to do & why and they will tell you what you have to do and why.
They have sent me the instructions on how to repower walkers with whatever engine I had on hand.
makes a difference when there is a Mr Walker or two walking around the factory and not an alouf board of directors.