I knew of the Imperial being a separate make, but the car was usually referred to as a "Chrysler Imperial" by most of the people I knew...my father retired from Chrysler in 1989, and i always followed the company's practices closely. It was a separate entity from 1955-1970, then became a Chrysler Imperial again in '71...kinda confusing, and I'm sure the public noticed. Maybe that's why sales were never so great.
1964-1966 Imperials were popular demolotion derby cars around here for awhile...a sad end for such a magnificent automobile.
Dan