I have a 75 CJ and I have the H.U. in the dash, all you need is a decent deck with detachable face. If the face is gone the deck is useless.

As for speakers, I have a pair of Kenwood 6x9's on the wheel wells in the back (got the speakerless boxes at walmart for like $15 or $20 each) For the front I got a set of Infinity Kappa's. For the dome tweeters I got a hole saw and permanently mounted them in the dash, and for the 5.5's I got the centra-pod that goes on the floor in front of the shifter.

Let me tell you it is loud, clear and sounds really good. Bass is a little lacking, so now I am trying to figure out where to mount the 10" DB driver. (that will probably go under the driver seat in a custom made box.

I never get into mud. I rarely get into water that deep, if you do, keep in mind what wyleone said about the centra-pod.

Good Luck!