Ok, working on this project and discovered that the speaker one of the previous owners had installed is busted.  What do you recommend for a speaker and what is the best way to mount it i.e face down, on the side of the cab etc.

Easiest thing to do is drive 5 minutes up the 174 and pick up a Midway style speaker for cheap in my garage, or grab a 9X6 inch from a store somewhere. Are they 9X6 inch?  I could be wrong. But I'm definitely not wrong about having working ones in my garage.