my friend owns a shop in torrance california..he has the RB motors for sale in fact few months back i was gonna buy the RB26 but didnt want to go through with the modification...well i saw the RB25 and 26 motors sitting there and im pretty sure he can get more if they are sold. he gets them straight from japan and are tested before ship. i dont have the number in hand but you can do a search on www.google.com just type in GSPEED or maybe G-SPEED and it should get you a number to call...take it easy..if you get the motor pls inform us all about it...my friend is putting the RB20DET motor in his 240z so when that gets done it should be nice...he got the front clip of a R32 skyline with the RB20 motor in it for about 2000-2500 dollars. good luck on the swap!
RB series engines are made by Nissan and most commmonly are found in Skylines and Cefiros, they come in 2, 2.5, 2.6 and 3L varieties, the RB30s are not double overhead cam though. The 2.6L twin turbo engines are the Skyline GTR engines and are well known for going up to 1200 odd hp with lots of mods and money invested. Stock an RB25 or RB26 turbo or twin turbo is around 280hp.