its on a k engine I'm guessing?
should be just four nuts on the front of the fan pull the fan off and put the nuts back on to hold the pulley there.
zip tie the thermo the the radiator and wire it up through a switch is easiest.. or can wire to the ignition.
both fans do the same thing.. but thermo does it better and also uses less engine power. both suck air through the radiator and on to the engine.. the standard engine fan controls the heat of the engine instead of just cooling it. by letting the engine warm up faster... which isnt to simple to set up with a thermo.. but its not really a big deal...
and if ur worried about turnin over the engine you should be able to use the nut on the crankshaft pulley.