Assuming you optimise your tuneup, sounds like you are close, the change to 3.55 gears will amaze you. A little annoying on the highway with small tires but really effective for accelleration!
First thing to do is to close the plug gap to 045, even the factory did this shortly after introducing the hei. They found it just was to many problems at 060 gap.
double check the internals on the hei if its a used one, not unusual for them to be rusted or dried grease preventing any centrifical advance movement at all. Often a good cleaning and relubing inside with minor disassembly required and they will work like new.
One way to check overall timing and advance function, if you havent already done so, is to observe the movement of the timing marks with the light while slowly speeding up the motor by hand.
Its not unusual to pickup 5-20 honest HP by getting the timing curve right for your car.
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 My Daddy bought me a car but all I got was this old Pontiac.
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