Step 1: Scoring a Nifty Lookin Hi-Fi
When buying your retro-stereo, try to have an idea in mind what you want to do with it, and make sure that the layout of your "antique" won't make your modifications impossible. My Hi-Fi originally had volume and tone knobs and a huge blank panel in-between where I'd eventually put the CD control buttons.
Have a vision . . . it'll make your life easier!