I have installed three sets in TT rears.  Trust me on this,  take the thrust 
blocks out and have someone with a lathe face the tit off of the blocks that 
were caused by the centering hole of the old axle.  If you don't, two things 
will happen, once you set the end play it will become excessive in 400 or 
500 miles after the tit starts to wear down ( the reason is the centering 
holes in the old axles were larger in diameter than they are in the flanged 
axles) and second you won't have to use as many shims for the end play 
setup.

Ron Butts