Hi! I have what appears to be a factory prototype of the early 70's earthwood 6 string flattop guitar. It is stamped inside "factory prototype 661". I have contacted Ernie Ball customer service directly with little info obtained...was hopping some of the experts here could give me some info! I know they made a short lived run of the earthwood 6 string around 1972... At least I thinks that's correct. This guitar would seem to pre date that. Any help would be most appreciated!