Hi Will. The MDL Converter is used to convert 3rd party aircraft created with FS Design Studio (or AF99) for FS2000 to display external weapons in CFS2. Aircraft posted in the CFS2 sections
should be already converted. This is not always the case for earlier models posted on the first few pages of the CFS2 sections.
PS. See my reply to one of your other posts for using the CFS1 defaults in CFS2.* I'm having a job keeping up with all these questions. LOL

*PPS. I notice that Mathias already answered that.