LOL, your an idiot.
Why would he want to buy a stock rb20 and put it back in.... Isnt the point in modifying getting more power :S
Doesnt the Rb25 come stock with 20kw over the RB20??. Is the torque not higher becuase its an extra .5ltr in capacity? Is the engine not 5 years newer??? I honestly dont get what your trying to get at??? If money was such a problem then he would have gone the cheap way... ffs some people these days.