1966 dart front brakes?

If you still have your old parts, just compare the new to the old. If they don't match then you have the wrong parts. IIRC, your car should have 9" X 2-1/2" in the front, 9" X 2" rear . Measured across the face of the shoes and inside of the drum. Not the outside.

Your first upgrade would be 10" A-body drums. Next step would be K-H discs. Both retain the small 5x4" bolt pattern.

The biggest Chrysler drum brakes I remember were 11" X 3" on the front of some 60's c-bodies and hi-po b-bodies.

3-1/2? Never happened.