Hello Garbs,
In general, I believe the answer is No.
In some very limited cases depending on the tool used to create the model, it may be possible to do something but it is unlikely.
The cases I am thinking of are models that may have been built with AD2000 and were originally for CFS1 and then modified for CFS2.
In the general case, even if you can get the model to appear in the aircraft selection, the textures probably will not because CFS1 is limited to 256x256 bit textures.
The model itself probably will not display correctly because CFS1 uses an earlier version of DirectX and must have all viewing planes (Glue) defined in the model itself. The result is that the model will look like an X-ray view of an aircraft with many internal parts viewable from outside.
That means that even if it is a AD2000 model originally intended for CFS, unless you have the CFS textures, the CFS2 textures are not likely to map correctly. It may be possible to go through the model's code to correct the mapping but it would be tedious at best.
Just as a matter of note, most of us here actually build with Aircraft Factory 99 which builds models for Flight Simulator 98 and not for Combat Flight Simulator. That is why animations don't work in multi player and bomb loads don't work at all.
We do some limited corrections in the SCASM code to make things not so ugly but the models are still basically for FS98.
Hope that makes sense.
- Ivan.
P.S. Just out of curiosity, what is is that you are looking for in CFS1?