ej257 case or shortblock

I am Looking at putting a ej25 turbo into my car and having it built by my local subaru shop they were telling me about a budget build were I bring in a case and they put full internals and all for about 2.5 grand. I was looking on flAtirons for a case and saw the stock sti short block for 800 more than the case. I'm looking for about 300 to 350 whp can the stock shortblock take this reliably?
Thanks