He's getting lucky. Sounds like he is a competent tuner. That helps.
But...you can only do that so long. That's why the X block was made. The T/A blocks were failing at a rate of 90% (IIRC) and those engines were around 600-650 HP. A stock 360 will never be close to a T/A block, let alone an X block in rigidity, ring seal, bearing life etc.
