Keep in mind, if the sc cltuch draws [dissipates] 47 watts, a circuit with a designed in capacity of approx 50 watts may not last too long. I would add a larger fudge factor .... 47 watts x 200 % would be safer (so two 50 watt resistors in parallel).

also, this difference may seem trivial, but I would consider basing your calcs on running voltage (14) not battery voltage.
As you probably know ... resistance = voltage squared divided by watts .... so the difference between 12 and 14 volts becomes the difference between 144 and 196 in this equation.

keep up the cool work,
Chris

EDIT
if you are limited by Fry's inventory,

you could put two 10 ohm 25 watt resistors and one 30 ohm 25 watt resistor in parallel

for a total of 4.29 ohms

this should create a 3.2 amp load (close enough to the 3.3 amp load that your WIS info suggests) ... your dissipation capacity will not be great (58 watts? ... this is a marginal fudge factor).

Finally, you might want to ask someone to measure the current draw on their sc clutch and work it from that direction.
Chris