According to the parts book, all 318, 340 AND 340 3-2bbl have the same pulley if its a Federal pump. 2951901. Also according to the parts book, the pump on a 340 with 3-2 bbl is the same pump as a c body with a big block. It was discussed that the federal pump had different valving for the more pressure required for the BB and fast steering ration.
So. The pulley I just bought from a TA is the same diameter as the one I personally removed years ago from a 340 Challenger, 6 and 15/16”. They both have the same vendor number of 82668. The TA pulley is dated 3199 and the cooler is 0210 these are both common dates for the TA/AAR cars on there coolers and pulleys.