Get the model numbers for all the units you are looking at and then look at the IPL to identify which parts you need and which parts are the same. This is what we have to do.
I was looking at Sears parts direct. They only sell a small fraction of the mower parts so it’s not good for getting all part numbers but the illustrations are good
The owners manuals by model are pretty good and have part numbers. I guess in my case if I wanted to check if a 48” deck would fit on my model that came with 54”I would get need to work back to the frame parts and lifting components to see if those are common
