I reckon if push came to shove I could gut an original radio, and make all it's knobs and buttons act as "steering wheel" controls for a modern unit. How cool would that be! Speakers you'd have to creative. Mount small piezo tweeters up high (off the sunvisor brackets), bigger midrange units in the kick panels (like a WB) and a tube/box subwoofer behind the seats. There is enough room behind the seats to fit small amps, and those long box subs have an inbuilt amp so only need a pre-out from the head unit to drive them. If you buy a good head unit these will drive the piezo and midranges fine, just use a pre-out for the sub woofer(s). I'm not talking about doof-doof hat back-to-front wanker subs, just small ones to give you some bass which you won't get from the midranges. If you have a van you could use the side panels for subs if you like too.