Pull the lid off of the heater box under the hood and see how cool the heater core is. It should be almost as warm as the radiator, equally across it. If it were mine, I would replace it anyway. My 64 would burn you out and I never covered the radiator, don't believe in it,
Scott

Scott Ward

2 1948 1.5-ton Loadmasters
The red one and The snow pusher
1 1950 3100
1 1955.1 Chevy 6500
1 1954 Chevy 6500 2-Ton
1 1955 1st Series COE 5700
1 1963 K20 (454)
1 1964 C10 (350)
1 1951 1.5-ton Dump Truck
1953 and a 1956 Ford F800

Raising a teenager is like trying to nail Jello to a tree!