It is part the process in changing a timing belt. If you look at the instruction for changing a timing belt you can stop once you reach that point. It does not require removing the timing belt though just most of the pulleys, Idler belts and if you want to be safe the radiator.
The bolt holding the pulley and harmonic balancer can be tough to get out, and getting an impact wrench in there to pull that bolt is almost imposible without removing the radiator. The engine crank will turn freely as well which compounds the difficulty.
http://www.ehow.com/video_4978619_timing-belt-replacement-remove-harmonic.html
http://www.justanswer.com/Ford/143nf-replace-timing-chain-1989-ford-ranger.html
Behind the harmonic balancer. You will need to remove the right front tire, remove the access panel to the engine (through the wheel well), remove engine belt, remove harmonic balancer & pulley with a puller. Remove & replace crank sensor, align sensor with an alignment tool, replace balancer with an installer tool.. BE VERY careful with the balancer, the backside of it has a hall effect style blades. bending these blades will junk the balancer.
On the harmonic balancer/driverside
The crank sensor is located behind the Harmonic balancer. Try not to break the rubber within the Harmonic balancer when removing or on the safe side replace both the Crank sensor and the Harmonic balancer ( the big pulley on the bottom - most part of the engine.)
They are on the harmonic balancer but are they on the drivers side or on the passenger side?
at the front of the engine,next to the harmonic balancer
Easiest way is with an air impact. There are strap clamps available that would go around the harmonic balancer that would hold it while the bolt was tightened.
If you look at the harmonic balance you will see on the front of it a medium size circle. That will be your timing mark.
The "Harmonic Balancer", is found under the hood, its the biggest pulley on the bottom of the engine, there are three drivebelts, one for the fan and waterpump, ac and alternator.
Normal right hand thread. Counter clock wise to loosen.
The Crankshaft sensor is located behind the Harmonic Balancer on the front-passenger side
take off the right wheel and the cover wall and you wll see it
the oil filter is on the driver side front next to or almost completely under the harmonic balancer, best accessed from under the front