I have MM full lengths. They aren't just connecters, they are actually subframes. They go from the firewall to the torque boxes, and even have a block that goes between the subframe and the tq box, hard to expalain. They take more effort to install, and may require a little bending.
I had mine installed at a Mustang Shop, Mustang Services in Marietta, GA, and they said they were the beefiest, strongest subframes they had ever installed, but also the hardest to install. They charged $60 to install not knowing what was up, I tiped the guy and extra $20 for doing such a good job and not being a dick about it.