Truck wont go into gear

I just replaced the transfer case on my '89 GMC with one from an auto wrecker off a '94. Both are NP241's. I believe them to be compatible. I replaced the old one because it leaked severley. Now my truck will not move. I shift into reverse, or drive and nothing. (Not even that small drop in rpm to tell the truck is in a gear) Doesn't matter whether I try it in 4hi 4low or 2wd. When I go back to park, It grinds and the speedo actually begins to register a bit of acceleration, then it usually quickly clicks into park and the grinding stops. I'm not sure what I did wrong! Please help! Thank you.