I personally have imported some JK 3dos ships into XWA... like Goz studios Corellian Corvette and General Ramos Carrack Cruiser.

Sometime ago Spaceboy from Goz Studios used some opts converted into 3ds (using the opt to 3ds program) to import them as a 3do for JK... and worked well, he released the Razorback some time ago. It shouldn't be hard to import the Valiant into JK using the correct editor's tools.

And as you can see on those screenshots of JK Tactical Assault MOD:

http://jkhub.massassi.net/project/show.php?projid=140§ion=screenshots

Importing XWA and XWAupgrade models into JK is quite straight forward...

The limit of XWA's engine is even thinner than JK's engine, i think, as the limit per mesh is usually at 200 triangles to avoid crashes to desktop while ingame, and a max of 256x256 pixels fo a 256 color texture.

Well, in fact that facecount limit has become rather obsolete by now. The Valiant has some meshes with >500 faces and works perfectly (as does another little something a buddy and I are currently working on...).