gmc vs. chevy cabs difference

[one wing angel]

Hi Folks I am hoping someone can give me a timely response to this question.
Are the 47 -53 Chevrolet and gmc cabs the same. I have a 51 gmc on the radar and would like to purchase it if.. ? the truck in question can be modified to a 51 Chevrolet version,
..do the fenders, grill hood etc interchange.

I have done a quick search of the forums but quite honestly, got bogged down in the responses. too much information that was irrelevant...

thanks for your help in advance,
John