The 1:1 El Camino version was called the Black Knight in 78 and Royal Knight in 79. It had hood graphics a lot like the Firebird's "flaming chicken" design. I can't remember if it had a "Don Quixote" type graphic on the tailgate or not..I kinda think it did.
Phoenix Graphics, an aftermarket supplier, makes a "Black Knight" set for a 1:1 El Camino.
A quick web search took me to this page:
http://www.hobbylinc.com/htm/rmx/rmx852979.htm
It describes the 78 Revell/Monogram El Camino Lowrider kit as including the Black Knight decals.
hth,