If your rubber washers are too soft, you may actually INCREASE vibration at the radiator mounts. Vibration is a weird thing. I think I'd be more comfortable with solidly mounting the radiator to the core with maybe the exception of some thin material to isolate the aluminum from the steel. You might find nylon washers with a sleeve to isolate the bolt from the hole in the radiator. Your truck being a 1952 it should have the more rigid radiator support with cross braces.
