ok i have a 3 channle f body and my friend has a 4 channle i want to put his 9inch in my car what will happen and what will be the difference!?!?

 

they do too
I have both ABS ant TCS both work great an have a moser 9"

 

You will have no rear ABS or TCS. The difference is, a 4 channell uses reluctor wheels on the the axle ends to sense wheel speed, and a 3 channel uses a reluctor wheel on the ring gear, which currently is unavailable on a 9" gear, without some custom machining.