After my '72 center stand broke the second time (I was alleged to be only going about 85mph for about 10 lousy miles!), my mechanic recommended the 850 center stand. It's more sturdy and I have not had any more problems with it. Since the 850 uses bushings on the mounting bolts, I did need to enlarge the holes in the frame plate, but that was relatively easy to do. I also had to drill a new hole in the 850 stand for the spring as the 850 mounts the spring in a different location.
Someone with more experience should give their advice as to whether the 750 spring should be replaced with the 850 one.