Ok, I think I got this sorted. Nate at
Equipment Parts Sales helped me figure it out. EPS has a bunch of NOS driveshaft, and he was really helpful and patient with all my questions.
Basically, it looks like there are three NSN numbers for the LMTV FWD driveshaft (P/N 483-49-050-145)
NSN: 2520-01-545-0390
NSN: 2520-01-478-7612
NSN: 2320-01-447-3884
Nate was nice enough to photograph each one and measure it for me. NSN: 2520-01-545-0390 matched my existing driveshaft exactly. It looks just like the one I have, too.
I believe that the other NSN parts would likely work and might even be superior in some respect because, as coachgeo mentioned, if they fit MRAP and FMTV, they are evidently high capacity and modern. That being said, I went with the one that matched what my truck already had.
Michael