If the radiator and heater core held together with a 16# cap, a 4# shouldn't be any problem. Those are the parts affected. 4# cap was introduce on trucks in 52.
Things to do to lower the temp include:
1. Getting the radiator boiled to clean out the junk.
2. Back flushing the block. Also be sure that water will flow out the drain cock on the block, if not, clean out the watter passage with some wire.
3. Major tune-up that includes adjusting the valves and checking the timing, both can raise the engine temp if they're off.
