53 vs 54 front fenders

[Fred n' Ethel]

What are the differences between the 53 and the 54 front fenders ?
The pic is from the Classic catalog.
Only things I see is maybe a radius as opposed to a more square corner where the grill goes in and the signal light ? Hard to tell though.
And, what should I look at to tell the difference when looking at used parts at a swap meet ?
Lastly, can one be readily made to work in place of the other ?
Till now, I thought they were the same.
Thanks.