Working with what you have and getting what you want do not often go hand in hand.
With a 600hp big block you are going to have balance issues (front end weight) not to mention power that will easily overwhelm the normal suspension mods usually talked about here.
I don't know what your end goal is exactly but lets say for example .
You want to be able to hang with a stock, mid 90s, 130hp, Miata on the twisty back roads .
It isn't going to happen without lots of mods .. Probably the replacement of the entire front suspension and k-member along with working with someone to balance out the rear suspension. Then you will need to get a tire/wheel package under the car that will both grip and not be blown away every time you put your foot in it a little.
One way of going fast is never having to slow down.