Looking to buy/build 500-600 fwhp 360

So is appears there are no crate motors that are built for about 1 hp per C.I., and also able to take a 200 hp shot of nitrous. I'm going to have to find a machine shop that will put one together. I have a couple of shops in mind.
Blueprint engines tell me good 360's are getting hard to find. Should I try to sell my good running 360 already in the car, and look for a block? Or should use my current engine as a core because I know what I have? It has about 10k miles on it. We've had it about 30 years.