Several things:
#1
My dad had a 75 V8 Valiant (100% sure) and it had drums (98% sure). I remember thinking it was odd for a 75 as I thought drums were done (100% sure that memory is associated with that car).
#2
Rock Auto is showing the same brake hose for 69-78 C-body and Formal cars (and others). HAs that vendor made the hose longer to fit more cars? Who knows in the will-fit world.
#3
When converting drums to disc you MUST relocate the frame bracket for the brake hose, otherwise the hose will be tight at full droop/full turn of the wheel. Quite possibly those of us doing brakes are installing hoses in such a scenario. 69-73 use the same caliper, and 69-73 are similar subframes, so I don't think there's a difference in the 73 hose. Oh, there could be, but how would the factory have gained from that?
#4
Over the years I have used 2 sets of braided E-body brake hoses on my cars, and they work like a champ with no adapters or anything. On 1 car it was the sole upgrade to my brakes, and the pedal did seem to feel firmer than before. Other car was a full susp rebuild/disc swap so too many variables. Cost is fairly reasonable, too, when you subtract $30 for 3 rubber hoses.
And BTW - learned #3-4 prior to the internet, got it from looking at where-used catalogs in Napa. Did my 1st disc conversion back in 92 or 93...