well the standard "Add disks to your A body with drums" set up is the later claw slider caliper disk set up used on later 70s US A/MFJ body cars
now that is just a slightly bigger version of what you get on a VJ valiant a Girling Lockheed style single piston caliper on a claw like bracket
you can buy the parts from rockauto
and when i say bigger i mean that the caliper is about 1/16 of an inch different so it won't fit onto an Aussie claw slider bracket used on the VJ VK.
i.e the VJ caliper is local and you can get some off an Aussie Val. id do that and bolt them to the US stub axle and use a US hub/rotor
other option would be second hand 4 pot calipers and rotors off say a 68 barracuda with disks but expensive and hard to find and rotors work on small inner bearing stubs as far as i know.... if your duster has disks currently it has a stub with an inner taper for a bigger inner hub bearing than an Aussie valiant uses.
you could fashion something or buy a kit that uses viper calipers... at least its all mopar
keep in mind that your upper ball joints are the bigger ones (don't fit aussie stubs)
if you already have disks on the car the stub axle you have has a wider taper for the inner hub bearing so Aussie rotors won't fit as they are small inner bearing rotors.
you could use Aussie calipers but you'd need US rotors
alternatively you can fit US stuff to an aussie stub, the caliper brackets and caliper will fit
but your need the inner bearings sleeves from Dr Diff to use US rotors and you'd need aussie upper arms and balljoints or you'd need to ream out the upper ball joint taper to use the 74 upper arm and balljoint currently on the car
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I guess the first thing i should have asked is what are you upgrading from and what do you want to achieve
your modern hemi is probably lighter than what was there previously
and if it has disks already i'd look to get them working right, designed for narrow crossply equipped 70s car. with radial tyres, get some proper proportioning in place first and see how ya go
otherwise
Brakes :: Front
you could try
Home - Hoppers Stoppers Custom Brake Upgrades
other option is sumitomo calipers off a landcruiser hilux 4 pot caliper with the same mounting as a valiant some messing to convert metric holes to imperial sized mounting bolt and you need imperial to metric brake pipes.. i can supply details
Dave