Front Driveshaft length

I have customer who swapped an 03 nv5600 into a 99 2500 with a 241dhd case. He needs a front driveshaft as the one he had got slung. I can't seem to figure out which shaft to give him. I thought an 00-02 6 speed shaft should work, but it's about 6" short. Any help would be appreciated!

Then sounds like u have an 00-02 5 speed shaft. The 6 speed is 6" longer than a nv4500. And a nv5600 is no diff in a 2nd gen or a 3rd.