I was just looking through the VP files associated with the Zathrus 2.8 package, and I found a couple of Aurora models that appear to be be based on the high-poly model, but reskinned for the PSI Aurora, and another that's listed as the "Line" Aurora, which I assume to be the MK1. The models in the 3.6 release are 1986 KB for the base model, and 683 KB for the PSI and MK1, while in the Zathrus package, there are said models at 2135 KB. I compared the standard issue models from both packages, and despite the 150 KB difference, they appear to be the same model. The Zathrus package also has models for Ivanova, Sinclair, and Sheridan, which I assume are simple reskins, and since you're not gonna have more than one each in a mission, a simple texture replacement in FRED would accomplish the same thing. In regards to the PSI and MK1 (Line?) models, if they are better than those in the 3.6 release, you may want to swap them out.