Were you not asking about cam's the other day?
Why do you want a rebuild? I can't help but think you are just a dreamer, you seem to ask a lot of silly questions, how many of these things have you actually had done?
By all means ask a question if theres something you want to get done soon, but constant threads about things you have planned for "next year" start to get a little boring.
As Rob said already if there is issues with your car, start off by addressing those First rather than a hypothetical race car build!
And in all honesty, if you want to build a beast why not start off with something better than a high mileage FWD a4, if youve got the money to pour into the engine bay then maybe consider atleast selling and buying a quattro varient. As much as we all try to deny it, the b7's are starting to become a bit long in the tooth now and can be snapped up fOr a lot less money they we like to admit, so by shopping around you could probably get a reasonable quattro varient for not much more than a FWD. A much better platform to build on if power is your thing.