Sorry, your pics come across (to me) kinda small, so not so easy for me to see what's going on. Regardless, on the topic of assist arms - I have a reman Coates machine with assist arm. Can you live without the assist arm? I have a friend who says yes, but personally, I call
BS. The Coates assist arm has saved my a** several times. I often mount 45 series tires. My opinion - I use the arm mostly for pushing DOWN, and only occasionally for pulling up. I do not have a "disk" assist thing - not sure if that would be a bonus or not. But I do use the assist arm for pushing down, every single time that I mount a tire. For small trailer tires, or "grandma" 80 series tires, you can probably get away without any assist arm.
If you want to chat further, shoot me a PM. I'm a racer also...