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Eddie, I have these heads on my 1970. Can't tell you what the "before and After" picture is since they were put on a fresh engine with many other street modifications. Dyno tests in magazines such as CHP indicate a good value.
Be aware that: 1.)these heads require a different intake manifold than most SB heads. I don't know how many different types of manifolds are now available for these heads. I've got a Performer RPM for Vortec - it's a higher intake than the stock cast-iron job and clearance could be a problem with a stock 68-72 small-block hood. 2.)no heat crossover in either heads or Performer RPM intake. Not a issue if your driving is primarily warm weather. You'll also need to go to an electric choke. 3.) these heads have center-bolt valve covers.
Hope this helps a bit with your decision.
Be aware that: 1.)these heads require a different intake manifold than most SB heads. I don't know how many different types of manifolds are now available for these heads. I've got a Performer RPM for Vortec - it's a higher intake than the stock cast-iron job and clearance could be a problem with a stock 68-72 small-block hood. 2.)no heat crossover in either heads or Performer RPM intake. Not a issue if your driving is primarily warm weather. You'll also need to go to an electric choke. 3.) these heads have center-bolt valve covers.
Hope this helps a bit with your decision.