Not a mistake here, just the facts, “were chosen for specific engine and transmission combinations” correct, the 335 horse power 383HP used in B & E-bodies in ’70 & 71 came from factory with Holley 4160s. Transmission, N96, non-N96 variants identified by list numbers. The 383 4bbl engine installed into C-bodies had Carter AVS’s, as the factory replacement parts catalogs from the time clearly indicates. The mymopar.com listing you linked does not show any Holley 4-barrel carbs for ’70-71 383 HPs, that is simply not accurate. I suggest you look at other sources for more accurate info that should include the already referenced factory documents/manuals for correct info. The use of Holley 4160s on this ’71 b-body 383HP application has been well documented over the years, a simple search on this forum alone will result with numerus past discussions on this topic, dating back years.
As for the carline codes, fact is, P, D, C, &Y carline codes all refer to c-bodies only period. Not only have I owned and dealer serviced these cars dating back to when they were new, also did a stint in various parts departments selling replacement parts at dealers, trained and paid to correctly interpret the factory parts catalogs. Your repeated interpretation of these codes is flat out wrong.
Wing nut? Another vote here for AMK Products, closest I’ve found to originally used hardware.