Four Wheel Drive Won't Engage

[LF_MN_71GMC]

Hey guys, I have a 71 GMC 4x4 half ton with a NP205. Here's the problem. I suspected the four wheel drive was not working so I put it on jack stands to test it. I can see both front drive shafts turning when in four wheel drive. However, neither wheel rotates.

I figured this was due to the locking hubs not making contact on the driveshaft splines so I took the hub off and manually slid the locking portion onto the splines and tried again. This was to ensure the shaft was locked onto the rotating assembly.

Result, now the drive shaft won't rotate when engaged. I remove the manual engagement locking portion and the drive shaft spins again. Thoughts?

Any help would be great.