Did your family member know your audacious goal of 500HP when he started?
Focus your money on the heads. If I was going to try and achieve 500HP I would ditch the Vortecs (and I do LOVE Vortec heads). Get some nice aluminum ones and plan on spending $1,200+.
You are not going to get to 500HP on an RV cam. Nor is an RV cam suited for super/turbo charger. You need to get one suited for forced induction. Also you are going to need a roller cam and full roller rockers. Both these will probably net you 50HP+ and some MPG. A solid lifter is also going to help you get to your power (and you are going to have to adjust valve lash every 3,000 miles).
What pistons do you have? I hope for the $3,000 you have invested thus far you have some flat tops (factory dished pistons are not good for performance).