"general rules that describe what carb goes into what engine/tranny combo are found in the FSM"

The factory service manuals do not define “rules” as what engine/trans combo is used in what body line. As already posted in the wing nut thread, the FSM only provides information about processes and specifications necessary to service and maintain the various vehicle components, arranged by component groupings, or systems, and covering the FSM’s brand (Dodge or Chrysler/Plymouth FSM) full body line. The factory parts catalogs sole function is to accurately define factory replacement part numbers based on the original part applications. In this case, once the correct carline code is understood and applied, the ’71 parts catalog clearly shows the 6125S was used on a 383 variant used for C-bodies only and all B&E body 383HP applications having Holleys originally. Any third-party documentation that counters this, or fails to show any Holleys, is just wrong.