4wd moving woes

[old Rusty C10]

truck is a 79 k10 longbed th350 trans NP203 t case.
truck was running and driving for days. I park it and put on the plow. it snows 20 plus inches a couple of weeks ago so I hop in try and put it in four low and it wont move all I hear is like grinding of gears . Call up a buddy and he comes over. we jacked up the truck and tried moving the levers on the transfer case and no matter what we did you could push the truck forward and backward even if the trans was in park. Figuring the transfer case was bad I went out and put in a used transfer case. now we can get the truck to act like its in park but if we fool with the levers no matter where we put them it appears that the transfer case is in neutral... sometimes we can get the wheels to turn a fraction of a turn ( while up on jackstands) nothing on the floor When we took out the transfer case it appeared the trans was good no play in the tailshaft. we had 27 splines on the output shaft and the gear in the case.. Any ideas? anyone close wants to look at this thing for me?