One of my "thought projects" has been to extend the bumper about a foot back. This would let me encapsulate the hitch and provide a longer diffuser for the belly pan. Practically speaking, this might not be easy as the deeper bumper has to be strong enough to stand on for loading/unloading. But if the rear taper (6-10" total) isn't big enough to make a significant improvement in FE, then a 12" extension on the bumper probably isn't going to improve things enough to matter either.
For taillights, I have side marker LEDs that I will install once I have the taper figured out. I'll just follow the DOT rules for lighting with turn signals. Cars like the Corvette have no taillight visibility beyond 90 degrees, and they are legal with the side marker light.
Regarding the grill block and fan, I have avoided doing anything with that until I have a reliable temperature gauge readout. Since it's OBD-1, all I currently have is a dumb sweep gauge that goes all over the place depending on whether the AC is on, if it's at idle, coasting, etc. I have a plan to add a "real" gauge with digital readout, I just haven't built it yet. It'll happen soon, as I want to get temp readings in the summer to be sure I'm capturing worst case under load.
I have an electric fan set up that's ready to install. I might actually go over to my local dyno and run a with/without stock fan test, just for fun.
