There was more than one Simplex bolster design too. The TLT truck
is one. I have a hi-res 1967 picture of an SP flanger that has very
different looking bolsters, but cast into the face is SIMPLEX. (The
trucks are very interesting, appear to have a combination wood and
steel spring plank for example, and an extremely odd spring package.)
A completely different animal, Jon. The Simplex cast steel bolster
was introduced around the turn of the 20th century by the Simplex
Railway Appliance Co., which had disappeared by the early 1920s.