Bellhousing alignment is a critical item. There is a section in the factory service manuals just on this item. Now some history on alignments. On both automatics and manual shift trans the factory spec is .007" total runout. The reason this should be checked is every time a block is lined honed the crank line is moved approximately .004 to .006 " to get everything straight. What this does is moves the crank centerline farther up in the block. Now I have been doing this check for over 30 years. It started for me trying to get a front seal leaking trans fluid. I have done them in the car and on the bench when building new motors. Probably 75% of the engines I have done needed the offset dowels. I have even had brand new aftermarket blocks that did not meet the spec. That goes for all 3 Chrysler, Chev and Ford. Every motor that I build the first thing I do is when the crank is in it I bolt a bell housing on it and check. The factory service manual give detailed instructions on doing this procedure. The factory makes offset dowels on .007, .014, and .021. Now these offset dowels are also in the aftermarket and I personally use ones made in Nevada.
