There is only 1 reason I can think of to use a 1990-94 2.2 Subie.    The reason is to pass the California smog test since CARB does not allow any OBD2 Subaru engines to be legally transplanted into Vanagons, even the latest Subaru PZEV engines (Partial Zero Emission Vehicle) that are in the same category as the Prius.

If you register your van outside of California and want Subie power, find a late model 2.5 engine....don't bother with an old 2.2

The California smog test is stupid.   You can fail because they don't like the engine you chose, even though what comes out of the tailpipe is 500% cleaner than a waterboxer.

So people in California who want legal Subaru power have to use tired old Subie engines from 1990-94, or at least 90-94 intake and control systems on a newer 2.2 long block.

To learn about LEV, PZEV, SULEV, etc you can read this article;
http://www.canadiandriver.com/2009/03/25/auto-tech-subaru�s-pzev-vehicles.htm