The difference between a standard bore (4.233") and "boring" it to 4.250" is only 4 cubic inches. You'd never know the difference. With that being said, there's a lot more piston/ring options out there for a 4.250", which is only .017" over.
A 600 hp 482 will require aftermarket heads, BBM, SM, Pond, etc. By the time you pay $3000-4000 for an NOS 427 block, you're looking at close to $17-18k for a turn-key engine that will make that much horsepower.
Personally, I'd go the stroked 390 route. Some Cobra replicas will fare better with a true "427". Some will do just fine with a stroked FE.