What Jimmy said is exactly what I've found. On most engines you can have 29-31* ignition timing, and another 26* to make it work. I've found no other cam where I've need to run less than 28* and get it to run like this, but occasionally, you find one that takes something out of the box to make work.
I recently got in an engine from another builder that I suspect was using this cam, or possibly his own close variation of it, and it had very low timing as well. It doesn't work on all 04-3 engines, but certainly more than a one off anomaly.
You can question it all you want, but when it runs out on the dyno AND on the track, you stop questioning and just believe.
I'm a little stiffer on IN pressures than Jimmy (generally) and softer, or the same, on the exhaust.
It also depends on if you're using a 1.485 - 1.500" spring or one of the WMS style HD springs. Installed pressure is one thing, but nose pressure @ max lift also figures in to where that valve starts to float and how much it controls it.
Once you get it right, you duplicate it in that block forever.
And no, there's no one size fits all on spring pressures either. Just tons of trial and error until you get it right.