First go to here to identify what model you are looking at: Previous Model Year Product Information
If the information is not in the brochure, then go here to dig further into the particulars of that model: Manuals & Diagrams
In 1995, depending on model and options, the chassis would either be a Chevy P30 with 454, Chevy P30 with a 6.5L diesel, Ford F53 with a 460, or Oshkosh chassis with a 5.9L diesel. Workhorse did not start selling the P30 chassis until 1999.
Once you know what it has, then use the search feature to find info on that model exhaust header replacement.