Apparently, since the stovebolt crankshaft does not have a flange that protrudes much past the back of the block, clearance between the flex plate and the block becomes an issue. Rather than grinding the block, which is obviously an irreversible procedure, it makes a LOT more sense to simply install a shim to keep the flex plate from rubbing. Be sure to account for the thrust bearing clearance which allows a very slight fore-aft movement of the crankshaft, usually .005" or a bit more. There's enough wiggle room in the pump drive slot on the converter to handle some flex plate shimming without any concern. Just make sure there's room to bolt everything together without bottoming the converter hub in the inner pump gear. The closer the better, but don't take up ALL the fore-aft clearance.
Jerry


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