amsoil and Accell make oil foam air filters. You will need to clean them, but they should solve your dust problem. (Accel only makes a 6 cyl one. Amsoil has both 6 and 4)
In high dirt environments oil foam is as good as it gets. Don't think so? when was the last time anyone here cleaned out the filter on thier Briggs & Stratton. I'll bet the thing still runs even tho it's burried in crud.
I won't use K&N in high dirt. If you study K&N's own data you'll find they let thru quite a bit of trash. K&N is only at it's best filtration when it's dirty. Oil foam on the other hand is good from clean untill plugged nearly solid.