Chevy ran 60-61, then 62-66, because of the bubble nose hood.
GMC ran 60-62, then 63-66, also because the bubble nose but if you can find a 60-62 GMC hood buy it, they are pretty rare- not many made and most where scrapped because of wrecks and couldn't find a replacment.
But Chevy and GMC hoods will fit on to each other- all year 60-66.You just have to know what your looking at.
Just for kicks go to 6066gmctrucks.org and you'll see the 60-62 gmc hood then look at the 63-66 and look at the difference.
Jesse Hazell Chevy Duty Tech.