is it this simple?

I have a 32 gts-t with 230bhp@ the wheels with v.mild tuning but am looking for much more, I know i can get it with the rb20det but have been offered a rb25de engine complete and a set of GTR pistons. Is it as simple as changing the pistons i.e do they have to be used with GTR rods or not and are the rods not different lengths ? I will assume piston pin to crown height will remain the same.
G.