I would in addition to the alternator cut off switch put an a/c clutch cutoff on there. Mainly to help it go up hills. Also a light on the dash to indicate when the torque converter is locked up is really useful.
For stuff that actually costs money getting more power will help your mileage so maybe consider underdrive pullies. I would leave the plastic clutch fan on there since it generates a lot of heat with the heavy loads probably and it would need more air than an electric is going to flow probably. A shift kit to keep the transmission from slipping any and changing to synthetic fluids in the trans and rear end. It is probably TBI so a good home made cold air induction might be worth a bit of power and that means keeping it in 4th gear better which in turn means better mileage and less wear.
Just tossing ideas out there for you
