The swap over date is in the TSB I posted, listed as approximately November 1, 1972. After that all the front drums would have been the new 10x2.5” design with the new large ball joint drum spindle. There is no new 9” drum brake mentioned, and the new 10” drums were run with 9” drums in the rear, which is in the TSB.
Before the changeover, the start of ‘73 model year production would have been early August 1972, when Ma Mopar would have been using up the prior year small ball joint spindles and the 67-72 version of the 9” and 10” drums. Then switched to the new 10x2.5” drums and spindles November 1, with no mention of the new, redesigned 9” drums. Because that’s why the TSB came out, it announced the changeover from 67-72 drum parts to 73+ drums and spindles.
So you’re saying that Ma Mopar designed a brand new 9” drum set up, to use with the ‘73+ large ball joint, larger wheel bearing 10” drum spindle? Then left it out of the TSB describing the new 10” drums that used the same spindle?
Got part numbers or pictures?