I bought a guitar in the early 80's in a shop in munich (germany). According to my knowledge (and the invoice) it is a Guild S400 (I remember the guy in the shop telling me it is a S400AD, the A stands for Ash, the D stands for DiMarzio Pickups).
He told me they got it from the music fair in Frankfurt (it was a prototype he said), and I can say I immediately fell in love with and bought her.
According to their serial-database it is the last but one of the S300A-series build in 1979, but a friend of mine played in that time a S300D, and that was a different guitar. The body is the same, but pick-ups, pick-guard, electronics, switches and the bridge are different ....
You can see my baby on the pic, the only thing not original is the GK-3 pickup I added for my GR-20.