I did a summary of the changes to the temple recommend from a post done by Edward Kimball. Here’s my summary: https://wheatandtares.org/2019/05/22/temple-recommend-evolution/
I thought it was pretty interesting. In particular, the questions really shifted in the 80s toward more faith-based ones, probably in response to the claims we were not Christian. Additionally, most of the changes seemed to be an attempt to rein in bishops who were going too far rather than adding to the requirements (although some requirements definitely got stricter over time while others got looser or were dropped).