'70 E body knuckles will fit on an A body but it is a bad swap because those really aren't great brakes to use. The '70-'72 B body disc brakes (same as E body) are expensive. They also aren't big enough for performance use but will work okay on a mild performance street car.
E body cars were made from the parts bin. In '70-'72 they used B body stuff, in '73 to '74 they used A body parts for brakes.
The best knuckles are the '73+ big bearing spindles. You can buy brand new ones for $200 a pair from Doctor Diff. Used ones are getting a little harder to find in wrecking yards. The later model FMJ knuckles also work fine and are a little easier to find.
