Lots of good advice given thus far.
Here’s my only addition.
A GMC dash has one hump, on the driver side, over the instrument cluster. The Chevy dash for 60-63 has two humps.
Changing the dash in a cab is a huge ordeal, so I vote for a GMC cab if the dash and ID plate both agree.
I’ve attached a pic of a GMC dash.
CHEVY DASH REMOVAL VIDEO