Can a 1990 subaru 2.2 be used in a 2002 subaru ?

Legally? No. You cannot go backwards to an earlier engine in a newer vehicle w/o making all the emission control work as they do in the original installation. This is Federal Law, whether or not your state chooses to ignoret. There is possibly an exception if you surrender the street plates and registration and instead have an "Off road" or "For Competition Only" certificate issued. Some states don't even do that, but eventually they will. California, for instance, issues a "Greenie" registration for those situations. Your results may vary.