Here's an even better question; what manufacturer would Arco Electronics have sourced their OT's from? Did they have a catalog back then? It seems reasonable that Jose would have used something readily available to him from his suppliers. Cerrum or Plexified, do you have any knowledge on Jose's company "Arco Electronics" back then? It seems more probable that it was an off the shelf part, but for all we know, this could be a small batch custom made for Ed by a 3rd party at Jose's request...good luck tracking that one down.

"TJB" says that Jose told him there was a transformer place over the hill form Jose's shop.
http://forum.metroamp.com/viewtopic.php?f=16&p=296601" onclick="window.open(this.href);return false;
Anyone know what this place is; what transformer Company is...or was "over the hill" from Jose's shop in Sherman Oaks, CA? It might be a good place to start. Mercury Magnetics is 15 miles away; that's one possibility I guess, and might explain why they have it listed as an "original design" on their website.