Thats an odd one....the body etc from a late 70's, but the neck (or perhaps just an inlay) from the early 70's. The schaller tuners seem to indicate late 70's too, and there's nothing to indicate others having been fitted at any point.
Most of the features seem late 70's...pots, bridge, tuners.
I'd say it was re-necked quite a long time ago. Its almost like a 'more typical construction' than that era usually has - solid body but with the mahogany neck.