I remember looking at that motor when I was going to swap a motor into a YZ450 frame I had built up. It was a huge and tall motor, def not going to fit into a frame designed for a 2T. I have a KX500 frame in my garage and I just can't see it happening reasonably. There's lots of unreasonable and expensive and time consuming ways to make anything happen, that's what machinists are for
The MZ used a 660 yamaha motor, see if you can visualize this in a kx frame cause I can't see it. Maybe if you butchered the frame but by that time you might as well start with a custom frame.