Okay here it goes my brother is in Iraq and i am tryin to finish his monte carlo for him myself. I keep getting the run around so i turn to you guys. Working on his 1981 monte carlo has 88000 miles on it. It has a 355 with headers x pipe and flowmasters. Had new 350 tranny in it with shift kit. It has the 2:73 single wheel peel in it i believe. I am wanting to get it to be posi trac with 3:73 it is his daliy driver when he is home and i think that will be okay for him even if he is running down the high way! But i need to know what do i need to do this i dont want to spend alot at all. I was told the guts out of a 82-87 s-10 would work? Can you please help me do this the cheapest way possible parts wise. Thank you for you help. oh and the spline i think is 26 i think whatever it came with. well please let me know  

yea you can use the gears out of a s10 i would just go to the junk yard and try to find one there itll be alot cheaper than going out and buying it new  

ya what jess said. all you need is a new pinion and ring gear. But dont forget to messure your backlash. If thats not done right your gonna have one noisy rear end! read the article on the camaro in this site. they did the same thing but its mostly for high torque output. not high speeds.