Yes, it is possible.
I have seen an RX8 with a V8 engine. No reason why you can't shoehorn an RB26:
https://www.youtube.com/watch?v=nCAkHAuC7Zw
But why you would want to do that is the big question. The 2nd most important question is "How much money do you have?"
Elms80 pointed out all the finer details.
you will not only just have to spend on engine but on custom drive shaft / custom bell housing, custom / modified transmission THEN contend with adjusted suspension front and back because now the weight distribution is no longer near 50:50. A 13B-MSP weighs 122KG - engine only. An RB26 weighs 250KGs - engine only. That extra 130 KGs so far forward on a 1.3 ton car has a huge impact to the handling characteristics. Furthermore, the RB26 transmission is another 100KG. Think about this a while - not only have you a fat ass engine right at the nose of this car but you also have a heavy transmission away from the center line.
Basically, every time you floor the accelerator, the ass of the car is going to squat so far back you'll see its panties. Every time you slam the brake, the front of the car is going to dive so hard, you'll be eyes deep in blacktop.
finally, you can buy an additional 2 RX8's by the time you are finished doing all that.