Just an update...the Bison rear bumper does NOT fit to the 660. I was able to attach the top bolts to the rack. However, The bottom ones were way, way, way off. I have cut the brackets off and will have the Bison bumper welded to my Grizzly and/or new brackets made.
For those of you asking, Why? I prefer the look of the Bison bumper for the Grizzly 700 over the Bison bumper for the 660. I will post pics soon.
In all honest, I prefer the Grizzly 700 HD front bumper over the 660 front grab bar, too. Maybe that will be my next project. Who Knows?