Installed used engine, now tranny doesn't work
 

I had a home mechanic install an engine in my 1993 Montero SR 4X4 with 3.0 V6 SOHC used engine from Japan after the original engine threw a rod at 154k mi. The engine starts and runs good, but now the transmission seems like it is not connected to the motor since I can shift into all the gears, but the car does not move and I hear a chattering noise from the tranny.

There were no previous tranny issues. What went wrong with the install? Did the mechanic install the torque converter incorrectly? Do I need a new tranny?

Thanks