Here's what the "shamrock" logo looked like on ND helmets in 1959 (top photo) and 1960 (bottom photo) -- you'll note the shamrock design changed quite dramatically. Who knows what ND was thinking with the top photo?
Rumor has it that Coach Kuharich put the upside down shamrock on the 1959 helmet to change the luck of the football program. I wonder what shamrock design the Irish will go with for the Michigan game?