Given that I was converting a 1e module, I mostly used the 1e Monster Manual as a source for inspiration when comparing abilities, as well as looking to other similar monsters in 5e to try and keep conversions more in the 'reskin / powerswap' realm as much as possible. While I have all of the editions' monster books, I didn't do a thorough analysis of each monster down through the ages to try and come up with the 5e version, but thus far when playing through this adventure with a group of 4 5th - 6th level characters, things seem to be about the right level of difficulty. Certainly some encounters are pretty easy, but I suspect a group of 5th - 6th level 1e characters wouldn't really have a tough time with 1e Bombardier Beetles either, so it is quite clear to me that the original module is intended to present encounters of a wide difficulty range, and that seems to be the case using the conversions I've posted.
