I haven't tried this myself, but I have a '68 Mustang.

I guess it depends on how you want to install it. The Mustang doesn't exactly have a normal DIN slot. I suppose you could try to craft your own bezel/frame so that the Empeg would fit in the factory slot, but I think that would be a total pain in the ass.

First, I'd recommend checking out the custom made stereos that are designed to fit in the factory stereo slot. Kenwood makes a bunch. I also believe Pioneer and Jensen even have ones too. I can get some links to these, if you'd like.

I'd contact the manufacturers and find out if any of the stereos support AUX-in. I find it pretty unlikely, but it's worth a shot. Otherwise, you'll probably have to run that stereo into the Empeg and let the Empeg be the primary head unit.

Now comes the other problem...where to mount the Empeg. My current stereo install (which was done by the previous owner) consists of the head unit just sitting on the hump between the two seats, directly under the dash. The owner put some velcro on the bottom of the sled to keep it in place. Not the nicest of solutions, but it works. A slightly better solution that I can think of off the top of my head is to get one of the "hump huggers" or other consoles that sit on the hump in between the two seats. Then, you could see about mounting the empeg into there.

Hope that helps.