Back to the subject... Not first person knowledge, but some relevant references.
For the 3 types of lifters used in '55, see
https://www.pontiacsafari.com/Servic...5-04-April.pdf, page 43.
For additional information on the lifters, see
https://www.pontiacsafari.com/Servic...55-06-June.pdf, page 75.
For differences between 55 & 56 lifters, see
https://www.pontiacsafari.com/Servic...09-October.pdf, page 102.