Is it practical to install brackets and outfit the McLane mower with a Weihle roller? Sure seems like that would help it do a better job. I looked at the front view on their web site and saw the small wheels. I do not have a good understanding of what the back end rides on.
Bet the OP's customer never dreamed they would stir things up to this extent. We may be able to get that yard down to 1 1/2" yet.