You're telling a guy that wants 600-700hp setup to invest the same money as a class racer who needs to make 1500. Any Joe Blow can tell somebody to get the best of the best parts available and spout out some things and stuff. That's not advice, plus there's misinformation in what you're saying. Gotta love the interwebs...so for clarity's sake:

The 6.2 Hellcat and 6.4 truck heads are made of 356 aluminum alloy with T6 heat treat and aging process and have built-in gusseting structure to maintain their structural integrity under high cylinder pressures. They are very stout pieces.
What are Thitek's made out of??? You guessed it....356-T6. Same material and he's boosting it. Have you priced a set of Thitek heads? They are $3000 BARE. Get a set of factory 6.4 truck or Hellcat heads.
All the other factory heads (early 5.7, 5.7 Eagle, 6.1, 6.4 Apache) are made out of 318 alloy, which is great for lower cylinder pressures but has a tendency to warp under boosted conditions. They just weren't made for a boosted application, that's all. They aren't made out of "crap" alloy.
And why would you have a set of heads CNC'ed when you're boosting the engine for a goal of 600-700hp. Hellcat guys are reaching 1000+, no porting.

Why spend the time and money to get a Hellcat block then put thousands into making a shortblock when you could just get an assembled Hellcat short block for less? As stated above, guys are pushing those engines well past his 600-700hp goal without issue.

Why get a special custom ground cam as well when your goal is at a the 600-700hp level. Hell, Hot Rod magazine took a 5.7 out of a junkyard, threw a $500 turbo on it and made like 630hp/690ft-lb with a total cost of $3900. Stock cam, stock "crappy" heads, stock internals.

My advice, get a used 6.4 truck long block. Same factory 356-T6 heads, same Hellcat block, more cubes allowing you to run even less boost for same power goal, use the stock cam, buy rods and pistons if you just can't resist, and you will have room to grow if you wanted to.