Looking to buy/build 500-600 fwhp 360

A 408 400 hp not a problem crate engines exceed that.
360 400 hp can be done but you will spend the $money that you can buy a crate engine for. If you can find one.
The car has a 360 with about 10k miles on it. It was from a rolled truck. It has been around my dad's shop for literally decades, but I've had it running well in this car a few years ago. But yes, if I'm going to go with an entire forged rotating assembly, might as well sell this motor and start with a crate motor.