Sense the V8 flywheels fit our 6s it gets a little weird. I have been told that the 168 tooth is used with clutches up to 12" and requires the bell housing mounted starter. It was used in trucks/pickups. The 153 is smaller uses up to a 10" clutch. It's starter mounts on the block. The problem with this info is that I know the later V8 pickup starter bolts to the block.
