A couple of thoughts...
How much does it weigh? What are you going to be doing with it? How about a model number and manufacturer as my take on HD may be different than yours. I have not seen a HD tiller with a chain drive -- they all go back to gear drive for the HD versions. They are kinda expensive for the HD models unless you are going to till several acres. The main parameter for most people is to be able to till out all traces of the tractor tires either by being wide enough or being offset to one side.
In my rocky soil a 5 ft HD tiller would probably be pretty hard on your tractor with 1000# bouncing up, down, and sideways.