Ok.. here is the skinny on RB conversions...
Rb26 is a big no-no. Extensive crossmember modification... different oil pan needed Rb25 tranny and a lot of electronics.
RB25 is much easier to do.. and it is already single turbo.. which is what you would have to do to the RB26 in the first place so whats the point?
RB20... (really... whats the point) why not just buy an SR ?

RB into a 240 is neat but really.. do you have the time and the money ? The RB powered 240s I ever saw were slower than dogpiss because of all the electronics issues.... they were still in the 14s. Hell you can get a stock SR 240 in the mid to high 12s stock ! Or you can do what I did sell the SR and get the mini-skyline motor. It looks identical to a RB motor except it is a 4 cylinder and shares everything with the skyline motor... and it can handle a lot of power.

later
martin s.