This is a old post and the problems have been taken care of! The twin tube down pipe I had was for a 2wd, not a 4wd. For some reason there is a slight variance between the 2wd and 4wd. I think what it is, might be that the R series bellhousings have just a little more beef to them. I'm not sure of this, because I never had a chance to match up the bellhousings to see!