Yep. Did it right before the Worlds. Nothing to it. Remove the old stuff with a dremel to within 1/4" of the fuselage (or closer if you dare) and install the new firewall. You will have to open the nose of the plane to 60mm for the motor to slide in from.

If you use this template, just change the side slots/openings to 2 each rather than single long ones. Then you shouldn't need the carbon support. [link=http://www.electric-f3a.com/Documents/Integral-Plettenberg%20firewall.pdf]firewall[/link]