Define "custom". It becomes a custom rifle as soon as it comes out of the box and you mount the scope of your choice. I have a couple of purpose built custom rifles. I have several "out of the box" Ruger Predators with a Boyds stock, a little trigger work that shoot just as accurately as I am...
We have one for our Ridgebacks. We also have a padded wrap around. We throw doggy blankets on them that are pretty heavy duty. Unfortunately they don't get a lot of use.
I'm pretty sure they are Millets like @mevertsen said. I found a couple other sets on fleabay and they look identical. They also look like they are going to be a major pain in the ass to get them aligned for windage. They appear to be polished stainless.