Oh, I think I figured out the answer to my own question. I didn't realize that the AR3 upgrade required all new steppers... :(

Here is a picture of my stepper for reference. I just ordered the steppers from stepperonline a while back for the AR2 robot.  Mounting-Encoder...

Thanks Chris! We got everything working well now. I'll post a video of one of our first tests in the builds forum. There is still a bit of adjusting t...