Finding resistors that can survive the wattage necessary to carry charging current is difficult. I used to make my own 1/4 ohm resistors for training purposed by purchasing four 1 ohm 100 WATT resistors, and wiring them in parallel with each other and connecting #6 wire test leads with heavy alligator clips to both ends of the resistor stack. Smaller wattage resistors will simply burn out in about 5 seconds. A 100 watt wire-wound resistor is about the diameter of a big ballpoint pen, and about 2 inches long, made of ceramic material with a piece of nickel-chrome wire wrapped around it. It is not something your local Radio Shack is going to have on the shelf. I had to special-order mine.

Yes, both current and voltage output needs to be adjusted. A Snap-On carbon-pile battery load tester is what I use to put enough load on the battery to get a good current regulator adjustment. Mine cost a little over $1,000.00. I gave you the shade tree method of approximating the tester load. Another method of getting the current regulator to max out is to put an almost totally-discharged battery in the vehicle, boost-starting with a second battery, and quickly raising the RPM. The generator will go to maximum current regulator output trying to charge the dead battery. You'll have 2-3 minutes of time to make the current adjustment before the battery begins to develop a surface charge and starts giving a false max current reading.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!