Well you've got the right block and I concur/defer with Pat, re; the heads. 700 horse is a lot of ponies to effectively street - not saying it can't be done and certainly the $15K is adequate however; you'll probably need to push 12:1 or better on your compression ratio to come away with 700 HP if you're going to stay naturally aspirated. A big BG Demon or a 1050 CFM Holley Dominator will do the trick there, but finding pump gas that gives you enough octane will be a challenge.

In that you're building from scratch and have the best possible block to start with, you can get real close on the deck clearance and fairly thin on the head gaskets to help get big horsepower. There's several ways to get to where you want to be and no one "right" way - but several wrong ways. Pat and Jerry build this stuff all the time and I'm sure they will have some suggestions as to machining but if you have a good engine builder, let him put together a quote for you and see what he comes up with.

I'd put some thought into cooling system to make sure there's enough radiator as high compression motors make a bunch of heat.