Trial and error my friend. No one here that I am aware of it running that type of power, nor am I aware of any reliable build with that type of power.
I would think a billet block would be the best bet overall, but I believe css<sleeve<billet

 

I already made 857whp but want more it's was advised that I strengthen the block

 

You will want to sleeve the block - CSS is good but you are dancing with big boys. If you want run with the big dogs you can’t **** with the puppies.

Sleeves with a larger bore and possibly are longer stoke … I think TCode has made over 1k hp and torque-sheared the input shaft of the transmission.

DesMax might be the only one with the ambition to go over 1100

 

My Friend Kyle made 1006whp with the CSS. He Also hold the 350Z Stick Shift Record at 9.33 @ 153mph, and the Standing 1/2 mile @ 183mph

I have a Built Motor but No CSS or Sleeves, just Cosworth Stopper Head Gaskets and L19 Studs with a Vortech making 850whp+