It would have something to do with where they put the zero and scale on the timing cover, wouldn't it? Different scale location would require a different mark placement on the balancer relative to the key? Weren't the early small blocks zero'd on the passenger side of the cover, which would require a different zero mark location?
Early forget what years pre 67? timing marks were on a bracket on the passenger side. That definitely would require a different mark on the damper. Way different not 6 degrees different.