To your question, Steven, I had zero idea when I started the process with Hileman, what I was looking for. I started by asking around (including here) what the easy cheats would be for a MkI Rabbit GTI - cam came back as number one since there are lots of cheap easy options that still idle OK, 2.0 bottom end (which would be visible externally, as there's a mark cast in the block, and the throttle body off of an Audi 5000 of the same age. I did some internet research and found pictures of the two parts, which (luckily) were visibly different from the outside since the bore diameter of the wrong one was so much bigger.
I decided in advance I didn't want to go so far as to tear anyone's junk completely down, but knowing that looking at the cam (the cheater versions of which would also have marks or evidence of where the marks were removed) wouldn't cost a ton or leave him with a pile of parts in the grass, I was prepared with a stack of 20's to do that.
I presented my protest with the items in order from cheap and easy to find, to pulling the cam cover. The stewards asked if it would be OK if they started with the visible issues and then if necessary came back for a bond to pop his top. Sure. Off the tech guy goes to make a housecall, with my paperwork and fee on file. 30 minutes later he's back. Guilty.
Short answer is that you have to do your homework. I recommend being strategic. It might sound like being a chickenshit to protest something that's minor but visible, but if you're confident someone is cheating, that will be a shot across their bow.
This topic comes up pretty regularly here, and in the paddock, and sadly we ARE influenced by reluctant stewards as well as the desire to not turn a fun weekend into a bummer. I didn't mention it but I also did my homework re: next steps if I'd been stonewalled by the guys/gals with whom I was supposed to file my complaint.
They are protestable, too. And they don't require a bond for teardown.
K
EDIT - I went to the SIC a few years ago ready to file a protest too, with specs and part numbers and stuff. I elected on that weekend to NOT file it because I frankly thought I was driving like crap and didn't deserve to beat the guy. There's no right decision for everyone.