A minor update on the boot last. It turns out that the measurement is off when I am making this boot last to fit inside the space on the outsole.
Even if I am able to sand the bottom of the last down to 11.5 inches, it will still clash with the inner walls of the outsole. So, I will have to make a compromise. Here are my options.
Option A: I would stick to the original plan and sand down the last together as one piece to get a uniformed fitting into the outsole.
Option B: I will have to sand down the walls on both the last and the inner walls of the outsole so I can fine tune the fitting of the two parts.
In the end, I may have to wind up using both options in an effort to get this going into the next stage, the molding process. I'll post an update in the future to share the results.