I got 10.6 CR without decking jack.
Needed to order custom pistons anyway, so got flat-tops and sized to basically be even with the deck.
Still have not found a legitimate reason for restricting
oil to the heads, at least not for street purposes, other than "that's what everyone says to do". Millions of FE's were built and lasted for billions of cummulative miles without restricting the
oil, or boring out the
oil passages. The thing you do need to watch out for it making sure the oil drainback passages are clear, and remain clear with all gaskets in place. Also, it's a pain, but try to get the oil 'fingers' installed, they help drainback too. You may need to experiment with different styles.
And I agree that getting 500 HP out of 428 cubic inches isn't as easy as some people think. A lot of people cheat and bore/stroke the engine out to high-400's or even more, call it a 427 and say its got 500 HP. Whoopteedo. Why the 500 number?
Especially with a 428? You'll want to spin things up pretty high to get that number (hence the recommendation vis a vis cams and lightweight valvetrain components).