Alright so...

you dont need a new manifold...you could run 425 hp on the stock motor...but its going to be a time bomb waiting to go( it really comes down to the tune) ...i personally wouldnt run more than 385 on the stock internals and such. if your gonna do something like add any type of power adder, you want it done right from the start

You can push that much hp with the stock internals but it is kinda hit and miss after 400rwhp. Some have been ok beyond 400 and others have come apart with less. The tune is what really matters so a good one is an absolute must. Its not the pistons that are the issue with the 2v its the rods that usually go before the pistons.

Also you dont need a new intake. There are a lot of people who are making over 500rwhp with the stock intake. I wouldnt consider upgrading untill you are knocking on the 600rwhp door.

I would not buy that kit from AM. Yes AM has great customer service and there is nothing wrong with the kit but IMOP its a little too much. You can get a better price from superchargersonline.com.

I would also just buy the base tuner kit from superchargersonline and gather the rest myself like injecters, fuel pump (the one that comes with the vortech kit is crap) and a dyno tune. I would then buy a nice front mount intercooler instead of running the vortech aftercooler. This will alow you more room to grow if you ever decide to build the bottom end and up the boost because the vortech piece is restrictive after 475rwhp or so. Its always better to do things once and not spend money twice just to upgrade to where you want to be.

What I am trying to say here is there are better ways of going about adding a supercharger then just buying a complete kit. If you want me to explain it better PM me.