Well brother you are trying to build a Big Block....there is nothing cheap...lol
First of all. CAN YOU TRUST WHERE YOU GOT THIS SHORT BLOCK? A free Big Block that has been "performance built" would make me a little nervous. You need to MAKE SURE without any doubt that what you THINK you have in that motor IS IN FACT what you have.

But you need to figure out how you want to make that power. Such as all motor? Or moderate motor and a good shot of N2O?
Also what is this motor being put in? race car? street car? daily driver?
The Performer 2 I would try and sell (just my honest opinion)
What transmission will you be wanting to run?
What rear end and gear ratio?
And what exactly is your budget?

I have known a lot of guys that have this target number with a motor, most new guys especially have big dreams of large numbers. But have you ever owned anything with some decent horses? I am not trying to deter you in anyway. But newer guys dont really understand what it takes to build 500 horses on a budget, and what it will take to maintain it. 3 years ago I built a "budget" stroker 496......$6000 later I was dropping her in my Camaro.....
500+ horses is a good motor. But do you have a transmission that can handle it? Will your rear end handle it? TRUST me 500 ponies will find ALL the weak spots.

Added Thought here: Do you want this 550 hp at the rear wheels or flywheel?