Unless the author (thicko) were to release the source code to you (very doubtful), it wouldn't matter, even if you did have GMAX. Also, since this was a CFS2 aircraft, it may have been done in FSDS (I don't have the model, so I don't know for sure).
Now if you just want to get it working in FSX, that doesn't require that you have any source code, just that you are able to overcome some of the normal port over problems, like having a solid prop disc rather than the normal looking prop blur effect, and opaque cockpit glass and so on.
Incidentally, I tried the link (which only gets you to flightsim.com, not the airplane), but after searching by aircraft name, author and a few others, the only thing I found was an update patch by Bob Chicilo. I never did find the actual airplane.