Anyone Running 215/70-15 tire on the front of a Duster?

Does anyone know where I could get 15x7 slotted rims for a 69' Dart.
The set I tried to mount has the wrong backspacing/offset, 3 inch.
Also, it has BBP and Disc brakes in the front. I can't find anything that'll fit!
The tire guy that mounted them said i can never put slotted rims on this car,
is there any truth in what he said?
Would 14" rims fit on a BBP 4.5 and would it work with the Disc brakes?
New to this, any help appreciated.