The tail-less variety is an offshoot breed of the original Halls Heeler, from what I have read, it was developed to remove some of the problems with the original line of dogs. In the link I posted above it explains a bit about the 2 lines, and there are links you can click on in the article to further drill down on some more details.
Kevins dog and the description of the Cowboy variety being crossed with a Corgi may explain the shorter looking legs.
Here is a link to more images of the breed -
https://www.google.com.au/search?q=...EvdvYAhVKwLwKHSXUBl0QsAQIJg&biw=2086&bih=1142
There is least one in there with no tail, also noticed a Dingo image as well on the 8th row ( orange dog ) this is the type of native dog that Hall bred with his original working dogs to create the Australian Cattle Dog/Heeler .