Transmission Rebuild

[dmigura]

I dont know if this is the right place to ask, but is a trubo 400 transmission hard to rebuild. I tried searching, but did not have any luck, must be doing something wrong. The transmission is in a 1980 3/4 ton 4x4 I recently aquired. The man I got it from said he got in it one day and it wouldnt move. I just got the motor running and put in gear and it made a god awful grinding noise it sounds to me it is coming from the tail on the 205 trasfer case. The truck doesnt even try to move. When I put it in park with the motor running it sounded worse as if you put it in park while it was still rolling. It is kind of hard troubleshooting when I dont know what happened originally. Also I took the drive shaft off and I could turn the output shaft with it in park. Doesnt seem right. It is just gonna be a ranch truck not worth a whole lot. So I thought maybe I could rebuild the transmission myself I have never done one before. So any recommendations would be appreciated. It may not be the transmission. Maybe something is broke in the transfer case. that is where all the racket is coming from I think. Is this a difficult rebuild.
Sorry for the long message, but I would appreciate any help yall may lend me.