man.. my tbird used to be the same way when we lived out in the middle of nowhere and had to drive 10 miles of dirt road to even get to the highway. dirt would get everywhere and my engine bay would look like the road its self. yeah, just take the filter off(get a screw driver and loosen up the screw on the thing thats holding it on, i forget what they are called) and take it to the parts stor you go to and say you need a new one, there shouldnt be any problem, they should know exacly what to get and if they dont, then they are the dumbest people on the face of the earth. the filter shouldnt cost too much, maybe 10-15(dunno how much k&n costs, just a guess). stick it on there and you should be good to go for another 3,000 miles(altho, driving it on a dirt road, just peek in and check it ever month or so) after that if you have an air compreser just blow it out when it gets a little dirty.
well, hope that helped.