Will a 72-76 grille fit in a 80 round headlight truck?

 

Those grilles are really different. If all you want to replace is the grille it won't work. But if you are up for swapping the lights and everything else then it should be fine (if you're asking if it will all bolt up to the rad support for example).

If you are just asking about the center section, the answer is no - that part is not interchangeable as far as I know. You'll need to swap more parts (which is easy to do).