AW4 causing engine to shake

My son swapped in a 96 aw4 into his 87 Comanche when he converted it to four wheel drive, and the engine has a bad vibration now (even at idle). He disconnected the torque converter from the flex plate and now there are no bad vibrations. We are planning on swapping the torque converter but could it be something else in the aw4 ? are there differences in the aw4 tourque converter between a 87 and a 96 ?
Thanks,
Dave