It's the tranny locator bore that is different. Nearly all of the SBC and I-6 Chevy bellhousings have either a 4-1/4" or 4-11/16" center bore. The SM465 needs a 5-1/8" center bore. I have found a site that says that casting number 3858403 has "a larger bore" , but it doesn't give a measurement, or say larger than what exactly.
Anyone know the answer to this? I hate to buy one and pay shipping without knowing what the bore size is up front. This would have been in a truck between '63 and '72 with the SM465 tranny and a 153 tooth flywheel. The starter would bolt to the flywheel, not the block.
