The Sportman"s Haven might be a great place but it seems to me that they could give you more information than "custom built". Did the gun have detachable sidelocks or was it a boxlock. Most of the AYS's if you order from them, you can order them with a straight grip or pistol grip, measurements to your order, case colored receiver or coin finish, double triggers, single selective trigger, beavertail or splinter. So don't let them tell you it was special ordered, they all are unless places like Cabela's, Bass Pro or Gander Mountain or any other big sporting goods chain orders them to what they think will sell.
Get all the information here.
http://www.aya-fineguns.com/ingles/modelos/paralelas.htm