Use
this one for cars with 5/8" heater hose, or
this one for cars with 1/2" heater hose. Most of the '70-'72 cars have 1/2" on the inlet side of the heater; pre-'70 and post-'72 cars mostly have 5/8""] for cars with 1/2" heater hose. Most of the '70-'72 cars have 1/2" on the inlet side of the heater; pre-'70 and post-'72 cars mostly have 5/8"