*INSERT RB30DET COMMENT HERE*
its seriously not worth the time or effort. Just to be difference doesnt really mean much these days. The guys who go for the rb26 to 2.7 or 2.8 sometimes regret it either due to lack of difference over the 2.6 and the cost...
If u must go this way 2.4 is with rb25 crank, rods, and them toyota pistons (i think it was 2gze ones??) that are factory forged. 2.4 is obtained with 2.6 crank, rods and pistons. U may be up for someones R&D which means $$.
Or u could buy a rb25de and slap it in using everything u have now (as well as the lower runners of the inlet as rb25de has bigger ports) and have yourself a 25 r32.
Or u could buy a $100 rb30 bottom end, slap on a rb25de head ($700) and continue to upgrade the mods as required...ie pfc, injectors, afm etc...THEN u will have a motor worthy of bragging how big your wang really is
If u really want to go for the rb30det route, pm me and i can send u the number of the guy who built Cubes' and my motors...