Graminal, one of my friends works at his dad's Volvo shop. If you want, I can ask him to find you an user 940 turbo box. Just make sure to block/reroute the heater hose inlet on the bottom. Another option is to use the box off a diesel Volvo.
A different idea: have you considered getting some aluminum sheetmetal and make a box that goes from the front of the car, a bit inboard off the headlight, and then turns right and ends in the fender? A circular hole would allow you to put your current airfilter. Some Volvo trunk weatherstripping would make it seal against the hood or something. I was just thinking on that since my friend did it on his Volvo and it seemed to work fine. After all, a flat piece of aluminum is easier to dress with some nice heat shield stuff.
What do you think?