Boo! What you see here is the Saito 100 a WM .40 size P-51 running a 12/12apc. Runs very good.
I have also assembled a few other of these same planes for some friends inclued the Dago. For the fire wall, I just mix up a combination of epoxy and milled fiberglass from Greatplanes. Slop it on the corners inside and out for added strength.

After I join the wings I cut the monokote back from each side of the joint enough to add a strip of fine fiberglass cloth/epoxy. Then cover it over with the matching sticky back covering. It will be nose heavy and I put the weight I need in the back side of the airscoop.

Also is the retracts, remove them and slop some of that epoxy mix insde their on the retract rails for added strength. I do this on all my planes. I have never had a retract rip out of a plane. I even stuff one once at full speed froma battery failure. The retract stayed in place ripping out all the ribs around it.

One of my other WM P-51's had a G90 mounted sideways with a Pitts style muffler underneath. Also iinstalled a 61fx in a Dago. That engine is something to consider also. I also had put some tri stock under the horizontal stab.

Everyone of these has been one smooth flying plane after trimming. On the elevator, it has one control rod coming out of the plane and to one side of the elevator. I changed it so that I still had one control road but added another wire so that it splits up when it comes out of the fuselage and the rod goes to each elevator.