Inadequate prior arrangements for formation flight by the pilot-in-command of the Cessna 182, N5434B, and his subsequent failure to see-and-avoid the Piper PA-28R, N5270T. Factors were: the Cessna pilot's visibility of the Piper impaired by the sun; restricted visibility for both aircraft due to low wing/high wing formation configuration; and the Piper pilot's attention diverted to other traffic.