The shape of the cowling on the 54 and early 55 trucks was the problem. A little rain past a leaky hood to cowl seal would run water onto the valve cover and down into the engine through the rear slots in the valve cover. if you want to solve the problem without doing any permanent modifications, just run a bead of RTV sealer over the rear slots near the cowling, and leave the front slots open. A solid cover and an oil filler cap with a filter in it does a better job of ventilating, and keeps dirt and dust from being drawn into the engine.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!