there's continuing debate and uncertainty about the exact shade of "gray" or "blue", grayish blue or blueish gray is what's generally reproduced I think, but with a 55-60 year old engine, unless the truck has very low miles, it's likely the engine has been repainted or the color is so worn it can't really be positively identified ..... the number stamped on the pad by the distributor and casting dates on the block and head can say if it's most likely original
Bill