I have seen a VG do a 6.6 in the 1/4 the motor was a monster. RB is inline and easier to work on and best of all a 70mm stroke, I would do an RB just to rev past 10,000rpm and to say I have a skyline motor too. Martin at XAT was talking about putting his RB into his z32 you might want to talk to XAT. I know they make special mounts now for it to get it in there fairly easy.