I appreciate all the input guys. I was thinking the cabs were the same but not certain on hoods and grilles. I was 99% sure fenders were different. As I said, the truck in question is 2 hours away so I can not easily get measurements and it is in a field purchased by people who aren't nearby either.
I have a '68 D500 out back and can see the cab/hood/grille are same as 1/2 tons of same vintage. The fenders are larger and there is a filler panel below the grille and between running boards and cab due to larger frame.
On the "truck-in-the-field", I can see from pics that the filler is there for the running boards but the weeds are too tall in front of the grille shell so I can't see if it is on top of the frame (like 1/2 tons) or if it is longer to cover the front of the frame.
Again, I am thankful for all the help.