I'm having a circa 1938 Paramount track frameset restored by Waterford, and have been shopping for components. The original Schwinn adjustable extension stems are next to impossible to find, and when they are available the asking prices are in the stratosphere.
I came across this reproduction in stainless steel for $149, and ordered one. It came today and the quality of the machining and the finish is superb.
I made a similar stem from some scrap I had lying around the shop. Not nearly as nice but it functions great for my beater bike, and the only thing I paid for was the socket head bolts. I'd like to try making a design with square tube like in one of the posts above some time.