There are several threads on here about the swap from pre 80 to 81+ or the other way around. I suggest reading them. As for the headlights, if you want round lights, you will need the 73-79 nose, you can not miss match parts. It must be swapped as a whole unit. Keep in mind also that it is a "mostly" bolt on swap, some mods need to be made, but are not too bad to do.
And just my opinion, best looking trucks were the 79 and older with 73-74 being the best. But that is just my opinion. Make your truck your own.