73 and up will work but the BJ on them are different and also the shafts are also are different. If it were me, and i wanted close or exact to stock, I would go with a 63-72 arm. This might be a good Opportunity to change to disc brakes.

1964 Chevy Crew Cab Longbed "Dad's ride!"
1965 C10 SWB LSx 4.8\4L60E My ride!
http://chevytrucks.stanleysparts.net/1965_swb.html