WeCole, you want to make a change to the truck to make a difference, think about this:
Take the stock bumper, shorten the frame rails by about 3". This will allow you to move the bumper back that same distance. Now, with the bumper remounted, cut the back edge of the bumper to reform the correct arc for the wheel well.
You will have shaved a few pounds off of the truck (about all that you would get from any custom bumper with the same crash protection), you have altered the aerodynamics of the truck (should help as you are forcing the air to make fewer changes (any directional change in air flow is what causes the resistance) and you have altered the appearance of the truck to be slightly different than other trucks. You would end up with a quazi 03+ look to your truck in a Gen 1 truck. If you wanted to take it a step further, you could find one of the front bumper covers and integrate that in with the grille and get a truely unique look. It would take a little bit of work, but that would make for even better aerodynamics if done right.
When it comes to aerodynamics, like i mentioned, changing direction is what is your enemy here (not so much size). In the case of a stock Gen 1 Expy, the air coming over the front of the truck hits the license plate, comes up, drops back some till it hits the grill, make a 3rd direction change to either go up and over the grille or to get through the grille into the engine bay. What air goes over the grille then makes another turn to go up and over the hood. Where if you can "flatten" the front of the truck, the air strikes the front of the truck, flows up and over the grille (minus what air goes into the engine bay) and then finally makes the turn to go over the hood. You start factoring in the little things like the gap between the bumper and the grille, irregularities in the grille face, etc, the number of direction changes can get rather huge.
Something to ponder. These are some of the things that I ponder when I am bored. When my mind is idle, it is the devil's playground. he he he he he he he.