1977 Chevy K10 4x4 Transmission/Transfer case locked

[JS1977K10]

I was in 4 wheel drive and after taking it out of 4 wheel, The engine seemed to bog down. I put it into park and heard some sounds. TH400 that was functioning fine, but now suddenly it will not go from Park into any gear. Behaves as though it's in neutral...

I can move the shifter freely if the linkage is not hooked up to the transmission. So I don’t think its in the steering column. It has transmission fluid. I can start the truck just wont go into gear once its running. Shift arm wont move from park to any gear.

 

[6872xtc]

Have you tried to rock the truck to make sure that there isn't excessive pressure on the park pawl in the transmission? Or is it on flat ground?
Sounds like there may be a problem in the transmission, if it won't shift out of park, you may need to drop the pan and investigate.

 

[Fordum]

Was the sounds you heard a sorta ratcheting or chattering sound possibly ending with a clunk? If so, the problem may be in your transfer case or linkage. If you put a transfer case in neutral, with the transmission in any gear and then try to shift into park, the output shaft of the transmission is still spinning and the parking pawl just bounces trying to engage.
But, in that case, odds are the truck will roll if on a hill or pushed.
Your description is a little vague, are you saying you disconnected the shift lever from the column and the lever on the side of the transmission will not move? I kinda sounds like your transfer case is either broken internally or in neutral. But that would not stop the transmission lever from moving.
The bogging down sounds like you were in 4wd on a hard surface road. That would cause drive train binding. I'm wondering if you did something to the transfer case linkage when you tried to shift while bound and it stopped in neutral. See if you can shift the transfer case into any other gear and if you feel it shifting.

 

[nvrenuf]

Based on the year - If you have a np203 tcase they are notorious for shifter issues. I would look at this closely to see if it's working correctly.