Yeah T3 is only the turbine housing general size and footprint, we need to know what the wheel sizes are an the a/r of the turbine.
A Gt35r with a T3 foot print can make quite a bit of power, last one I had on the dyno was on a 13b rotary, it did about 385 rwhp at around 15 psi. A rotary needs more turbo than a piston motor to make a given amount of power, so two GT35r's on a small block should make pretty big power.