Will the spindles, rotors and calipers from a 79 Newport fit an a-body?

the upper ball joint taper dia is larger on the C body so the spindle top tapered hole would be too big as is. Way back a C body UBJ has been grafted onto an A body UCA. Dont remember how they solved the spindle lower mounting bolts/lower ball joint difference on the lower end but it was not difficult. If you solved the upper prob I think mocking up the lower end would make the solution to that part probably pretty easy to figure out

a 79 Newport is an R body, which is the same as the late B's so yes the brakes will work on an A body. Provided you use the late A body upper control arm with the larger ball joint.

Spindles and rotors fit, calipers aren't a good idea because the hose routing will be wrong. Get the correct caliper for the application and you should be fine.

oops my mistake I thought that stuff was C body

The marketing guys at Chrysler went brain dead in the late 70's and badged a bunch of cars in silly ways. It is confusing trying to keep the names straight.