Al -
To add to what has already been posted, I have the 4V heads on my 71 and it runs plenty strong for the street. I had my ignition set per the engine compartment data plate and it ran like a dog. I believe the data plate says 6 to 8 degrees advance, change it to about 12 to 13 degrees advance. You may have weak valve springs and a worn timing chain also. I also have a mechanical roller cam with the matching springs and it will easily rev to 7000 rpm. You might want to spend your money on a new cam, lifters, springs etc.
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