What is the difference in a 60-62 and 63-66 C10 front bumper?

Well just as the title says can someone tell me the difference in a these bumpers. Trying to find a new front bumper for my C-10 and found one that says its for a 60-62 for pretty cheap in comparison to what else I am finding. Thanks!

 

maybe mounting holes....just looked on the Brothers Trucks site and they do list them as 60-62 then 63-66 but they do look identical....

 

i am not positive but the frames are dif. so my guess is mounting points.

 

yup, frames are different widths, mounting holes are different. Also the header (grille surround) has the slots for the frame in different places. learned that one the hard way