FS posi rear end
 

i have a rear end out of a 94 z28 i beleive it has 3:42 gears $250obo

Does it have the torque arm mounts on the driver's side?

yes

94 z28 M6 or A4? Im no LT1 guru, but i think if its an A4 its going to be 2.73 or 3.23 gears if it was a M6 3.42 gears. and is it a 3 or 4 channel rear? or backing plates?

the car had a 6 speed and im not sure about the rest

4 channel rears have the reluctor rings and sensors on the ends of the axles and 3 channel has it more in the middle of the rear. if it doesnt have either, it wont have any kind of rings/sensors on it. that should help ya!