None of the stuff listed will get you much change in power, depending on header design you can get torque earlier or later in RPM range but its the same torque as stock, thats the point of a tuned exhaust, to tune it to the RPM band you want the most torque in.
Stock exhaust is tuned, but for mid-range RPM band.
Electric rad fan will free up about 5HP
Underdrive pulley is OK, it would only amount to about 4HP-7HP on a 4.0l, 4 at 2,000rpm, 7 above 4,500rpm
Rangers(and all fuel injected engines) come with stock Cold Air Intakes(CAI), the add-on CAI can look much nicer, like chrome valve covers, but no change in power with either.
Mix ratio for gasoline is 14.7 parts air to 1 part fuel, this is a WEIGHT ratio, so 14.7 pounds of air for every 1 pound of fuel.
This is why "pre-vaporizers" are a joke, it is a weight ratio not a volume ratio.
If you add too much fuel you lose power, if you add too little fuel you actually gain power but it is very temporary because pistons will melt
You get more power from an engine by increasing its compression, or increasing the volume of the air it can use on each cycle.
A 4.0l engine uses 4 liters of air every 2 RPM, a 5.0l use 5 liters of air, a 5.0l engine has more power than a 4.0l because it can use more air so more fuel can be added.
A 4.0l with 9.7:1 compression will make 205HP on premium(91/93 octane) fuel
A 5.0l with 9.0:1 compression will make 210HP on premium fuel
But same 5.0l will make 210HP on regular(87 octane) fuel, the 4.0l 9.7:1 would PING like crazy on regular fuel, so..........you would be at about 160Hp
Compression is a double edged sword, on the one edge is the rebound effect, higher compression is like winding up a rubber band, the tighter you wind it the more power you get when you release it.
On the other edge is the fuel octane, octane is a heat rating, and higher compression equals higher heating of the air fuel mix when compressed.
8.6 to 9.2:1 ratio is about the limit for regular 87 octane fuel, above the 9.2:1 you start to get pre-detonation(pinging), 87 octane is igniting in the cylinder before spark plug fires, this will cause holes in pistons and burnt valves.
A bigger cam allows engine to pull in more air on intake stroke, so more air = more power
A supercharger(or turbo) increases the amount of air each cylinder is getting by forcing more air into the engine so you can add more fuel, 4.0l engine is now using 5 liters of air so more horse power.
These are just the Laws of Physics when applied to internal combustion engines, the more fuel you can burn on each cycle the more power you can make, but you have to stay with the 14:1 air:fuel ratio for gasoline engines.
better spark and cleaner air flow can make engine more efficient, an engine rated at 160HP, like the 4.0l OHV, might only be at 150HP with old spark plugs and dirty air filter, so those changes would get you more horse power, but all things being equal the changes just keep it the same.
Good 4.0l power stuff here: Tom Morana Racing Engines