I'm sure you know that United Specialties has been out of business for some time. I'd check with NRC or Showhauler. I think they build similar to United Specialties. I bet they could help you out.
'03 Freightliner FL112, 295" wheel base, with '03 United Specialties 26' living quarters, single screw, Cat C12 430 h/p 1650 torque, Eaton 10speed , 3.42 rear axle ratio