[Nick_R_23]

Stock type distributor? Might be a large part of your issue right there. The stock spring and weight combo was pretty conservative, and the stock HEI module will be limiting you, too. Unless you've had the distributor tuned for the engine, you're probably not getting anywhere near the timing advance that your engine needs, and those HEI modules are really only good for about 4500 RPM or so. Not to mention that if this is a used distributor, it may have enough wear i the shaft to affect the timing. I would recommend looking into a good aftermarket distributor and having your timing curve matched to the engine.