The Kodak Brownie Reflex Synchro model was manufactured from Sept 1941-May 1952 in the US and from 1946 to May 1960 in the UK; some were also made in Canada. Thus overall the model had a 20 year production run. The synchro model had a two-pin flash connector below the taking lens, and had the shutter selector inverted.
Through the Viewfinder photography (TtV) is a photographic technique in which a photograph is shot with one camera through the viewfinder of a second camera. The viewfinder thus acts as a kind of lens filter. The most popular method involves using a digital camera as the image taking camera and an intact twin-lens reflex camera (TLR) or pseudo-TLR as the "viewfinder" camera. TLRs typically have square waist-level viewfinders, with the viewfinder plane at 90 degrees to the image plane. The image in a TLR viewfinder is laterally reversed, i.e. it is a mirror image. Most photographers use a cardboard tube or similar 'contraption' to connect the two cameras. This serves to eliminate stray light and prevent reflections appearing on the viewfinder glass or on the lens of the imaging camera.
This one below is a calendar image that is going to be for sale at an Estate Sale this weekend - I hope I can get it!