rear brake upgrade on 70 dart

I agree with 68Dodge on going through the brake system, since our lives are in the balance based on properly working brakes.

If your front disc rotors have proper run-out / thickness within factory specs, you can stay with those. The K-H factory disc setup used 4 piston calipers, which tend to have rust problems in the piston bores, when the car is not driven regularly. My 1971 Duster 340 has the factory K-H discs, and the disc brake engagement is slow and lazy, if the car goes undriven for long periods.
The solution is to either rebuild/replace the calipers, and an upgrade is available to stainless steel cylinder bores with a lifetime warranty. Pistons, fluid transfer tubes, and piston seals are available, if you wish to rebuild. Brake line hoses are being manufactured in Argentina, and are on Ebay regularly. These brake line hoses may also be available from Fine Lines, along with new metal brake lines.

Many times, poor brake performance in A bodies is due to mis-adjustment in the rear brakes. The drums and the other components are available, try NAPA, or search this site for exact part numbers and availability.

I'd look at the rear brakes, rebuild as necessary, look at replacing the rear drum wheel cylinders, see Rich Ehrenberg on Moparts for upgrading to better wheel cylinders.

Hope this helps.

PS --- your car looks GREAT for $1,000! Looks like NO RUST! Wish we had those cars back on the East Coast.

Please post what your findings and repairs are, to fix your problems. Thanks!