In my opinion, the cockpit would be the trickiest part of any Mech to swap out. Imagine taking the cockpit out of a Boeing 747 produced in the '70's and installing it into a brand spanking new 787 dreamliner. This is the electronic heart of every Mech, where the life support, targeting, security, myomer control, electronic warfare, etc systems all come together. It would be a nightmare of cabling, junctions, connections, etc and would require the appropriate facilities for installation.