Changing cams alone is an RV and pickup truck thing; these engines deserve more consideration that just that. Given that you don't have build specs and dyno sheets I would go run it on a chassis dyno so you know what you really have. Your mildly-prepped 428 could be 400HP at the flywheel and considerably less at the rear wheels. I would then find an FE builder to talk to offline and discuss options based on how you want the car to behave when you push the pedal. As others have said you can put some money into it and get more power without breaking the bank or abandoning its purity.
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