would be interesting to see what is acheivable, but logically thinking the RB20 is only a 2.0L motor and u are putting twin turbos set up off an engine which has an extra 0.6L ontop iof it, which i reckon would put you behind the ball from the get go, not enough capacity to sustain the set up and will be a lag monster one would think.
RB25's are a popular conversion into R32's nowdays, they are bigger capacity motor and are apparently a bit stronger then the RB20 in stock form. plus not to mention they are a newer motor, failing that id go the RB26 if u can find a decent one about. butu u gota think of things like if u break the 25 its wont cost as much to replace as the 26, and or rebuild.