Hey Pete,
OldMech has it right. You can put a 3 in extension in between the mower and the tractor. A set of quick couplers will also help. You may need both.
Joel has told me another option - bolt a piece of flat steel under the length of the bar. It'll require finding a piece of ~5/16 steel and drilling some holes to line up with the bolts underneath.
The third option is a sickle mower weight that bolts to the to bolt holes under the shroud, but they're not a very good option. Supposedly the weight tends to shear off the bolts holding it on.
Bill in WI