Either block will work, 440 is a little easier to find intake manifolds for as well as headers. You might want to double check on both before you make a decision.

A 440 block with a 4.25 crank will get the job done. Get the heads ported so they flow 300+ at .600 lift. The .590 cam might get the job done. You only need 600 hp to go 10.20 at 3200 lbs so that is fairly easy trick for a 505 engine.

The 850 carb is fine for 600 hp. You need 1.4 cfm per hp so 600 hp is 840 cfm.

The CNC porting from 440Source should work fine or send the heads to Porter Racing Heads and have him fix you up. The Weiand intake should work okay at 600 hp.

Biggest decision is compression ratio. I'd probably shoot for something in the low 10's if you want to drive on pump gas. You can race on a mixture of unleaded premium and race gas or mix with Hot Rod 102 or something like that. If it is a race car only and you're willing to buy race fuel then increase the compression to 12:1 with a flat top piston and run race gas.

There are a bunch of tech articles that cover similiar engine builds. Take a look at my 505 article with a big flat tappet and slightly ported Edelbrock heads. That engine made about 650 hp and it would be very similiar to what you're trying to build.

http://www.moparmax.com/tech/2011/vi_8-flat-1.html