Found a shop near Seattle Washington that makes an adapter to fit 85-90 Buick Park Avenue front brakes to my 66 Valiant.
Name is Scarebird Classic Disc Brakes, should come up on an E-bay search, he has an E-bay store.
He has a lot of items for most Mopars, also an enteresting rear disc unit for B and E body.
Probably not the thing for you that want to stay all Mopar, and yes I get why you would, but worth looking at for those of us that want to upgrade without breaking the bank.
Take a look and tell me what you think.

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66 Valiant, 225.
84 Van, 225.
71 Maxi-Van, 318
60 Valiant wagon, 225
87 Maxi-Van, 318 4spd