I don't know anything about the option but it appears you're correct on the year - it wasn't in the 1973 accessorizer brochure but appeared in the 1974 and 1975 editions, and was listed in the 1976 general brochure.
http://oldcarbrochures.org/United%20...ure/index.html Of course they downsized the cars in 1977 so they were a totally different chassis and body.