Here is an outrunner conversion on my Typhoon. Ijust used some scrap plywood and balsa sticks Ihad laying around.
The firewall screws were used to keep it tight while epoxy dried up but I just left them in place. I used some dowels to further strengthen the mount to the firewall. You will notice end pieces of popsicle sticks glued to the fuselage so I could attach the cowl to it.

I use an E-flite Park 480 motor with a 10 X 5 prop. The 12 X 6 prop was way too much for this small plane. I would prefer an 11 X 4.7 or 11 X 3.5 for better hovering, so I'll be trying that next.

I crashed the plane on a windy day, trying to land. The prop hit the ground so hard that it broke the shaft on the Park 480 motor, but there was no damage to the plane or the mount conversion. So it proved to be quite strong. I do miss the sound of the gearbox, but I would never go back to a gear-driven set up.