Where I got this information from I don't quite remember, but the story went that Rick Neilson's Cheap Trick were on a tour of Japan in the 70s and Tokai Gakki entered into an endorsement arrangement with him and his vintage strats and teles(this may have also happened to his Gibsons) and their hardware were examined in great detail and replicated. Tokai reproduced the woodwork and the bridges which were pot metal at the time were supplied by a generic Japanese manufacture that produced strat bridges for a number of other strat copy manufacturers .The pickups specs were sent to Gotoh to produce pickups which replicated the originals as accurately as materials allowed. The same kind of grey board, and a similar number of windings with alnico 5 magnets with ground edges. The authentic sound and faithfull specs of these early Springys caused an absolute sensation in England at the time and the first batch sold out very quickly indeed. The E pickups were hand wound copies of some of his vintage strat pickups minus the cloth wire which was impossible to find in Japan at the time. The Us were the slightly hotter all machine wound mass produced versions of this vintage specced pickup. These were the pickups that wound up(pardon the pun)on the first Springys. How much truth there is in all this is open to question but It does have the ring of truth about it, (like a Springy or Goldie fitted with E stamped Pickups you might say!)PS the A stamped pickguard appeared on E loaded pickguards and B was stamped on U loaded pickguards.