Running the wires from the instrument panel to the back usually only involves pulling the side panels and then connecting and mounting the jacks. There are "indented" mounts that can go into the ash tray holes(throw those out) where the jacks will sit recessed and you won't be banging them each time you get in and out. Then you need to have a 4 place capable intercom mounted in the panel and connect that up to the 4 connections. It's about a day or 2 of work.
You might want to get an A&P to work with you so it is signed off.
If you don't already have a 4 place intercom I have seen the PM3000, softcom ATC-4PS, or the older 403MC work fine, but there are probably lots on the market for $250 to $400 and come with all the wires. I would get stereo so you can interface some music.
