Let's round him down to about 6 feet even to simplify, then he is about five muzzles high, so we can probably imagine each muzzle is about 7.2 inches (Probably inaccurate)
So if each muzzle is 7.2 inches at 6 pixels, each pixel probably is about 1.2 inches (Also probably inaccurate), and marc's muzzle in Swat's pic is 2471 pixels in length, equaling 2965.2 inches, and translated to feet.
Marc's muzzle is 247.1 feet long in Swat's edit
I have no idea if this is correct