Odd question about Dusters

"Kelsey-Hayes 4 piston '

Here I thought that these disks brake systems were far superior than the "standard" one piston system.

Grassy
On paper and in theory , the 4 piston Kelsey-Hayes brakes were supposed to be superior to the single piston setup ( and certainly far superior to yucky drums ) , but in application , they were trouble-prone .
My '72 Dart had those K-H brakes on it from 1972 - 1991 ( I owned it from 1989 - 1999 ) , and they fought me all of the time !

The pistons used to wear the pads unevenly ( as the pistons would stick in their bores , even after I had the bastards rebuilt !! ) , and the pistons would freeze in the bores , making the brakes dangerous at best !
I even switched to DOT 5 Silicone in 1990 ( after having the calipres
rebuilt ) , in order to cut down on corrosion ; nothing helped !

Parts were obsolete for those brakes for many , many years ( brake rotors were strictly UN-available !! ) ; now you can buy 'em all day long !

The single piston brakes of '70 & up ( B , E , F , M , J , R , ) , '74 & up C bodies ) and '73 - '76 ( A bodies ) are much , much better .

I think that the only reason why brake pads were available for those 4 piston calipres in later years is because the pre-1967 Mustangs used the same pads ( and same system , iirc ) .