Depending on what horn you get as a replacement (I put in a WOLO BadBoy), you may have to mount it on the back-side of the frame/panel/whatever you want to call it, instead of on the front, as the factory horn is.
I went the route of taking off the rocker-panel cover, then the driver-side of the front, and pulling it out of the way. No big deal, really (though I put the rocker-panel cover on the hard way afterwards), and it doesn't take all that long to do it.