Two Questions. rotors and a arms

[Clavo106]

trying to order parts... I have a 1971 c10 2wd 327.
Q's #1 now I dont know what the original a arm are from (yr)rubber stop not shure if its 1/2 or 3/4 ton are they the same a arms in length what tells them apart. can I just swap 3/4 ton ball joint and put 1/2 ball joint? if its the same arm?
Q's #2 can i swap a 1971 5 lug rotor and put a 1970 6 lug rotor on my spindel. i just bought a 1968 rear 1/2 12bolt rear 6 lug .i would like it to match the front.
thanks for any help givin"