What are you missing? That Ford often makes mistakes, and posts a disclaimer for such, in the consumer literature and listed part numbers in addition to not publishing every technical detail and differences between chassis models so proceed at your own risk.
Newmar lists the approximate CCC for a 2019 Baystar 3626 at approximately 3426 lbs. Where did the 1974 number come from? 3426 gives you 489 lbs for each seat belt. Newmar also makes mistakes in thier literature but I would expect the CCC of a Baystar 3626 to be fairly close to 3400 lbs +/- a few percent of the weight.