Complex sentence: In July 2008, a limited run of Chet Atkins 6120 Stereo guitars was introduced, based upon a 1956 prototype featured in several landmark Atkins recordings but never produced in quantity.
Split into simpler sentences: In July 2008, a limited run of Chet Atkins 6120 Stereo guitars was introduced. This model was based upon a famous prototype from 1956, which featured in several landmark Atkins recordings, but was never produced in quantity.