What VGT turbo to put on uprated ISX?

I had my DPF and EGR deleted on my 2009 ISX CM871 and it is now tuned up to over 600hp.

The turbo seals are going and I need to either rebuild or replace it.

My question is - is the turbo on a stock 455hp the same as the one on a stock 600hp? Do I need to replace this one while it's down with a larger one? Is there a larger one on the market?

I'd like to keep the stock appearance from the outside to keep the Cali Commies at bay... otherwise I'd go to another manifold and turbo altogether.

 

The aftermarket performance turbos are not VGT or resemble stock. I'm trying to stay stock in apperance with the best possible performance.

 

yes please, thank you!