As far as balance and blue printing the machine shop takes your crank,connecting,rods, and pistons and balances everything out so there is less vibration. Less vibration means longer engine life and less power loss through the vibration. Plus it allows the engine to rev easer and a bit higher. As far as a cam selection it depends what you want. You could go with a big cam and get that mean muscle car sound, lots of horsepower. But this comes at the expense of gas mileage, loss of torque, and drivabilty. It may also put your powerband so high that you may never see it. Hot Rod magazine Nov. 2001 issue had the best cam and intake combo. It stated that edelbrock air gap and xe258 cam by comp cams was the best real life set up, providing good power and drivability. They dynoed this setup 357@5,600hp and 370@4300 lb. ft. This was done with a gt40 crate engine.