The 2004R was never designed to deal with a worked BBB (500+HP), and a heavy car with perfect traction. Yes, there are great billet parts for them, and there are lots of builders who can build them to live behind big power. There are plenty of guys who run them with great success on the street and track. Like I said though, if I was worried about the weak link in your car, it would not be the rear, it would be the transmission. If your transmission is built for 600 HP, I would not worry about your rear given the intended usage. Just my opinion, I might be wrong.
Brian do you build full 12-bolts for other folks? I'm on the fence right now between a 9" or a 12-bolt on my 66. Either way I got I'd like a full inch more narrow on both sides for a total of 2" overall for some more tire room. 275/40-18 barely fits right now with rolled fenderwell lips so I'd like to have some room for error with disc brakes, etc. What's the cost on something like the 12-bolt that width with a 3.42/3.73 and a good posi? Thanks