stock hp is 275 with the tiny stock cam.
should make maybe 300 with the bigger cam.
330 with headers and exhaust
Are you going to put on a intake and carb or use the stock efi?
That engine has a factory roller cam so I hope your cam is also a roller cam.
You also need to modify your vortec heads to handle more lift.
I would also recommend doing a little DIY bowl smoothing on those vortec heads, especially around the exhaust ports.