Boys, listen to your Uncle JRR! The 915 and 516 are better stock heads.
If you have to do a $200 valve job on a pair of $600 heads, plus buy springs, then the Stealth is in no way nearly twice the cost of the "Indy" heads. And for a 425 hp 383 IMHO the springs that come on a Stealth head are adequate.

The Chrysler open chamber head was a compromise by Engineering trying to do emissions control on the cheap. It doesn't matter what fuel you use, it's a bad design.

Another thing, a 906 head stock will rarely see 230cfm with a good valve job, while a Stealth will see at least 260 out of the box. Plus the Stealth has a decent chamber, very much like the 915 head.

I'd suggest finding Dulcich's 383 build which beat the Chevy 383 in one of Enginemaster's online videos.

https://www.youtube.com/watch?v=L-uV61qilqU

Also buy AndyF's bigblock book. He'll use the money to pay for more dyno time.

There are so many ways to attain your goal that it makes my head spin.

R.