Im pretty sure the odometer has been wound back on mine too, so it could be anything really. But i know what you are saying, the RB engine has a reputation for being bulletproof.
I think the leaning out/detonation would be the most likely scenario, but dont know. I've owned the car for a year, and only covered about 15,000ks in it.
Nope, no smoke when idleing, it only seems to blow smoke when taken to about 6KRPM, i see a big puff in my rearview mirror.
It was dynoed about a year ago by the previous owner, i havent dynoed it myself yet.
Cheers,
Sam