On casting, you may simply want to send that head to someone who does it all the time. If not, I like high strength 3 mold making material because it is available at Hobby Lobby and I use a coupon every time. I also use the Alumalite resin fot the actual part. There are many tutorials on youtube.
Colin Jason Hobbs on face book, goes by Colins Customs, has made that exact vehicle and it is actually a fairly easy mod and a great one to start with. Best of luck and show us some wip pics.