Hey George!
Well as you propably know the blazer doors dont have the top section that the window rolls up into between the vent window and the back of the door. Even from the factory these were just sawed off with sawzalls. Then on top of that the factory added some braces to the door where the striker goes. They were added for extra strength due to the higher demands that were usually placed on blazer bodies. Unfortunately I dont have pictures of them but I will post pictures once I get them onto the donor doors.
The difference between truck doors and suburban doors are also tied to the top channel section. On a truck it is rounded and on a suburban it goes to a 90 degree angle.
I know these pictures aerent great but this is the original truck door before I started modifying it to be a blazer door. See how the top section (where the window rolls up into) is rounded.
On the suburban the same section goes to a 90 degree turn (no rounding).
And as you can see that entire section is missing from a blazer.
I dont know if this helps but if you want I can take better reference pictures for you to show you what I am talking about. Or if anyone else wants to post pictures fo the defferences they are more than welcome to.