My story... the 37 pickup I have originally had a set on it that I THOUGHT was original. Well, I later bought a 37 parts pickup from the original owners son after the truck had sat in the woods for some 30-40 years and I believe it was totally original. Well, the headlight stands on it was different from the ones on my 37 when I bought it.
Research says the ones on my first 37 were actually 38's and they ARE different from the ones off the truck I know to be original.
I once was going to sell the set I have as a 37, thinking they were, but just about everyone says they are 38. yes, they are longer than the 37's..... thats "my" story.
and yes, they do crack. Mostly the driver side. I filed a little ridge in both of the driver sides that I had, put in some JBWeld and the one on my pickup has held up well since.