Well sure... RB20DET is factory rated at about 220bhp, RB25DET is rated at 260bhp, and RB26DETT is rated at 276+bhp.
RB26DETT is where your getting into some complex shit though... But it is possible. You would have to get a BNR32's RB26DETT engine (1989-1993) and get an ECR33's RB25DET transmission. The two fit together perfectly, but only those two combinations will work, otherwise the clutch initiation is different.
... But dude, do you really feel like getting into all of that fabrication work? Ewww
I would say RB25DET would be the highest you would want to go... Otherwise your heading into some 'Monster Garage' project
But keep in mind... The R32 that you would be getting the RB20DET out of, will have weighed MUCH more than your 240Zed... The power to weight ratio on that RB20DET powered S30 would be INSANE... I say go for that, cheaper, and easier by far.
... But its up to you.
-Wes