I'm no expert, but it would seem to me that the V8 box would have - at least - stronger gearsets and a more robust valve body that the D5 and 3.2, in order to handle the extra engine torque available from the V8. The output of the V8 in XC90 / S80 standard configuration is very close to the torque limit of that (IMO weak) transmission, and AFAIK is the limiting factor with unleashing the vast potential of that engine.
AFAIK, the V8 'bellhousing' is unique; it's not a whiteblock bolt pattern, nor a Ford SHO pattern. Otherwise I daresay we'd have seen far more Volvo V8 swaps other than the S60 V8 Supercar racer, the Buchka "Fake Racecar", the 1800GT done with factory help, a Swedish 242 done by a Volvo employee, and the Noble megabuck sports car. So the 3.2 and D5 versions aren't going to bolt up. From the pics I've seen of this glass box, the 'bellhousing' is a bit more than just that; it looks like it may have a pump or something else in there, but please bear in mind my first 3 words here.