Have to add my advice on this topic
I just cant see the point of rebuilding and stroking the rb20, I love my rb20 and reckon its awesome for a 2tlr motor but at 250rwkw the gearbox becomes unreliable if it costs 5000 just to build the motor then your gonna need to upgrade ecu, turbo, intercooler, tune, etc.
Ive been searching around for a rb25det + gearbox and they cost around 3500 why not go the 25? it will be waaayyy more reliable and good for more power plus the extra torque.
Or you could do the rb30det option that cubes and bl4ck recommend, the later 2 options will be cheaper and give more power. Why go go through the drama of putting together an rb23/4?
My 2 cents