To clarify, the best ways to verify if it's a HR are check the redline (7.5k for the HR, lower for earlier engines) and dual intakes for the engine, as you can see in the engine bay pic on that ad.
As far as whether it's a good deal, the problem is that there is nothing to compare it to really as you mentioned, so you'll have to make a subjective assessment of whether it's worth it. Obviously pending verification of the mileage and that it's been looked after, which isn't a given just because the mileage is low. Good luck