That usually unreliable source of all ignorance, Wikipedia, offers this
"Dean Jeffries is an American custom vehicle designer, fabricator, stuntman and stunt coordinator for motion pictures and television programs based in Los Angeles, California."
If that is the one you are referring to, that's a pretty obscure connection with motoring history as we know it and hardly "an important figure in the automotive world"
I know you are a film fan, Ray, but many of us are not. Sorry but there it is.