Why did Dean Jeffries' Mantaray have a 289 Cobra engine? Cool story

Dean painted the first AC Cobra several times for Carroll Shelby.... painting it in different colors in order to fool magazine editors into thinking that many cars had been built... when actually only one prototype was.

So in appreciation Carroll gave Dean a 289 Cobra engine

Below is what it looked like in 1973 from http://www.huffreport.com/archives/oldpics/the70s.htm

photos from http://www.myrideisme.com/Blog/wp-content/uploads/2009/08/701.jpg
and http://www.ultimatecarpage.com/gallery/15647/Dean-Jeffries--Mantaray.html