Royal Oak Pontiac supplied a fully-modified "stock" GTO, 2+2 etc. for many magazine comparisons. Everything visible looked correct, everything inside that could help was massaged (head mill, narrow valve seats, blocked heat riser, new ignition curve, jetting, port matched).
I recall an internet story from what seems like eons ago. The fellow who claimed to have owned the 1973 SD455 Trans Am that went 13's for Car& Driver chimed in. His story was that car was a ringer. When they tore the engine down, it had low drag oil rings, the heads had been cut to bring the chambers to blueprint spec CC, and the intake had been port matched. There was even machinist's blue on the intake flange and intake side of the head. His story was that this was discovered on the engine's one and only tear down. True? Who knows. IIRC, there was some credibility, as he wasn't using a screen name, or there was another commenter who vouched.
