Jerry, the way I read Turbonator's post he's saying that the big hole machined in the back of the manifold to seat the distributor is machined larger than the corresponding dimension on the distributor shaft. I pointed out the JEG's bushing & shim set because the description also mentioned oversized distributor holes "...common to many aftermarket manifolds." Maybe I read it wrong.... I went out and pulled the HEI distributor and the hole in my manifold measures 1.3875" and the boss at he bottom of the distributor measures 1.20", a difference of 0.1875" or 3/16". Looks to me like the machined boss down towards the bottom of the distributor case, just above the drive gear, accomplishes the alignment, and once locked down on top the side clearance is not a big deal? Again, maybe I read it wrong.