The X-Mod was, somewhat predictably, created by -X-. He's not around any more and I don't think he left any contact details behind things.
If you're making a helicopter then I would actually suggest looking at SAV class over morphtank, and if I remember correctly there is a type of animation that's basically designed for rotating parts like rotors... though I am of course not an animator so that could be completely wrong.
Bummer, would've been cool to ask him some questions about the rotor type animation. I was reading some old posts on BZU that suggested it could be done using draw_geom or by dll.
I animated a rounded plane object in Truespace; it played okay in 3DEX but the XSI even though it had animation in BZ2 wouldn't show the animation play? Bummer!
PS: I watched quite a few videos about Coxxon's remodeled BZII project and was very impressed with the HD elements he incorporated into the game; quite visually stunning with new units and enhanced model detail.