RB25 and RB26, from what i see from different engine bays, quite different. Macam looking at GSR and Evo engines like that... both are very different from each other.
Thus probably RB25 and RB30 might share the same head design, or the very least, the mounting for the engine head is the same.
Since RB30 is a NA block, probably those with RB26 will use back their block due to difference in their material strength? And there are quite a lot of stroker kits for RB26, thus dun really need the RB30 block whereas stroker kits for RB25s not readily available?
But then again, they can get a RB30 and STROKE it again to 3.2l if and only if they have stroker kits....
But then yet again, i believe those researchers probably found out that the NA block ain't that strong to withstand high boost applications.
frank, i'm starting to sound like you... hahahha.....