Yeah that is going to take a heck of an engine combo to make 600 hp from a SB Mopar with a hyd roller cam. I did a 427 inch SB a few years back with ported Edelbrock heads. We used a small hyd roller since it was a street driven road race car. The cam was 236@050 and it made 520 hp. That engine might have made 600 hp with a bigger solid roller but I don't think even the biggest hyd roller would have made 600 hp. Maybe it would've, we never bothered to test it.

These days there are better heads available than what we were using so if you have a really good cylinder head you might be able to get there. Good luck, I think it will take some time and money.