Best way to proceed with improving up 427 Windsor street setup

[RET_COP]

If your only producing about 530HP from a 427 you have not experienced the full satisfying power of a well build 427. Something is very mismatched. Get the right parts and tune and if you get the true 585 you not only will pull from 2000rpms, it will scare you at 6500rpms in a 2500 lb. car.
I have a 351 with the right parts all sourced out to matched and I'm at 490FWHP or 1.4HP/CI. I can pull from 2000 rpms. to 6400rpms. 1.4HP/CI in a 427 is 597HP. Get your Carb, Intake, Heads, valvetrain,cam, and exhaust to match and you won't be disapointed, trust me.
I have great street manners also and you will too, and good gas mileage in the highway.
The easy way out is power adders. Like what was already said they work also, but you said you want the lumpy radical sound of a windsor, my advice will give you all of that

[Bernica]

IMHO, adding NOS or whatever is the chicken way out. Will give you more power but not solving the current issue and may even break something sooner.
My 2c

[RET_COP]

Agree Bernica, N/A all the way !!