I could not find where I saw them mentioned in the Ford literature, but if you have old copies of the Model A News from MARC, the July-August edition from 2016 has a write up about one. Page 34 shows the helper spring.
We are currently restoring a 255-A, and these springs are from the factory. We have them on ours as well. I will have to try and dig into some of the Model A books we have, but I believe they are mentioned in one of them. The judging standards do not talk about them, but there are some things...