If anyone is interested, I will be happy to share some hints that I have picked up.
Below is Ludwig 1960’s Serial Number Time Chart #1.
It contains particular number/date stamp pairs chosen from our original serial number index because they serve as good representations of the chronological trend of the serial number sequence.
By using this chart, you will be able to know in most cases the year, and time frame within the year, that your 1960’s Ludwig drum was made.
The drums I am trying to date are seven digits and start with either 1024, 1028 or 1755. My guess would be that 896xxx - 916xxx is the serial number span from 1972 to 1975, and not because they didn't make any drums during that time.