If it's encoded, then what you basically have is a two channel tape so you don't even need a quad reel to reel to play it (in stereo). You would take the stereo channels, feed them into a decoder which would output 4 channels if the source is indeed encoded, then send that decoded output to 4 channels of amplification and speakers.
If you just wanted to listen in stereo, you would be all set with a stereo reel to reel connected to a stereo receiver/speakers.
If you just wanted to listen in stereo, you would be all set with a stereo reel to reel connected to a stereo receiver/speakers.