I recently purchased my deuce with a 331 Hemi. I bought it from a dealer so there is very little history with it. I want to do an oil change and am wondering what oil to use. I currently use full synthetic in everything; am a firm believer in the high heat stability and lubricating properties. The whole zinc issue leaves me wondering what the proper oil is for an old (rebuilt) engine. Can is use synthetic and add zinc to it?