You'll find steel and aluminum versions of these lenses on trailers going back to the early 1950s.  This is the same shape as the old Tiger-Ey Hexflex No. 100.  

This reflector has an acrylic lens and a stamped aluminum base.  Mounting hole spacing is 3-31/32" and overall longest dimension is 4-11/16".  Overall depth is approximately 3/8".