You'd have to do a ton of modifications on the small head and 2 bolt block to get to 600. I would suggest you find a set of Police Interceptor heads and use these if you are serious about wanting to use a stock type motor....you can keep the oe look (no alum head) but install the large valves (1.75 and 2.25 ) and get a good starting place. Then raise the floors a bit to increase velocity and scavenge effect. Then, a stud girdle and some serious balancing on the short block to let it withstand the high rpm that will be required to get 600 hp. In all likelihood, the motor would be unstreetable in the end.
A more realistic street motor, without breaking the bank, would be a 500hp/500 lb ft stocker with the same setup as above minus the over the top machining. Keep the PI heads, add a roller cam and rockers, the stud girdle with a HV
oil pump and you'd have a serious street motor with a decent intake (the oe's intakes suck) and a well tuned carb.