I've got a 91 rs. It has the stock rear and and 2.73 gears. I'm building a 355 and plannin on getting 400 horses out of it. I'm getting the tranny built up to hold up. I need posi and a higher gear ratio. Do I need to get my rear end redone with posi and gears, or should I buy a whole new rear end. I'm tryin to watch what I spend but I don't want to have to worry about breaking my rear end. Any suggestions would be helpful.