How are you with photoshop?
I would find a whole bunch of (similarly oriented) 1951 Mays cards, download the pics, and then resize each one to make the images of Willie himself identical to each other. Then you can either put them in a column and look at the sizing of each one (does 'yours' look distinctly shorter than some or all of the others, etc.) to see if they generally match.
(Check out this thread to see what I am referring to:
https://www.net54baseball.com/showthread.php?t=226221)
Or you can lay each card on top of the others, align the pics of Mays, and then do a hide/show to see if 'yours' appears trimmed in comparison. Does that make sense?? It's how I create animated gifs now and again.
To be sure, it won't prove or disprove whether or not the cared has been trimmed, but it will certainly give you enough insight to either feel comfortable or make you head for the hills.