69 383 Performance
Before I would spend another nickle on it, I would check the cylinder pressure and perform a leakdown test on it, to see if you even have something to work with.
These should be the no1 go-to, anytime power is contemplated. You cannot make a silk purse out of a sows ear; And you cannot pull horsepower out of weak cylinder pressure.
See post #2, and others
The 383 should already be a ripper with the way it is, and with 3.23s, unless the pressure is down