I was in a situation somewhat similar. I passed a Motorist, he felt I wasn't entitled to a lane, swerved at me and tried to ram me. at the time I was new to my bike, and wasn't near as comfortable with speeding as I am today. I rocked the brakes and followed him. He did notice me following, and tried to brake check, and egg me on. I followed him down the freeway, and eventually observed a highway patrolman parked in the center median scoping for speeders. I pulled over, informed him of the situation, and gave him the license plate (prncs something, i don't remember it now). he told me he'd look into it, pulled out and headed in that direction. I never cought up to him again, so I don't know if anything came of it, but with a little luck you can provide chase and inform authorities without any fancy gear.