As mentioned earlier, the Coyote is physically a huge engine. The over head cams (4) make the top of the heads huge. I'm guessing, but I expect that any problem with the cams would require pulling the engine out to work on it. The variable timing on the cam shafts leave me wondering on the reliability, although I never heard of any problems. I would want to understand, if the variable valve timing can be worked on without pulling the engine.
The Coyote does not idle like a kitty cat. It has a rumble that you can hear changing as the rpms come down. Then it settles out fairly smooth, but sounds nice. When winding up through the gears it sounds great. I believe the Mustang has an X or H pipe in the exhaust. If so, it could sound very different with side pipes. With that all said, it is nothing like an old school engine sound.
The Windsor engine was a very reliable design. It is not prone to
oil leaks like the FE family. From what you have said, I would steer you toward an aftermarket 4.125" bore block with priority main bearing
oil system. I would have to compare the cost, but they are available with the 351 Cleveland main bearing diameter, which is better by some accounts (especially higher rpm). Stroke it to 427. Go with a hydraulic roller cam/lifters. Keep the duration on the mild side, with EFI in mind. I would be thinking around 228/234 duration with a 110 lobe separation angle. Keep the lift in the 0.550-0.575" range for reliability. Then top it with very good flowing heads to make up for the mild cam. Maybe AFR, with mild port work. Go with EFI. EFI is a huge subject in and of itself.
A Coyote is only in the 400-500 hp range. A Windsor based 427 in that Hp range with EFI is going to have very good manors driving on the street. The mild cam will have enough rumble at idle to let you know it's not your dad's station wagon.
Talk to Blykins. He builds engines every day. He tends to think a little more radical on the cam than me, but he knows more than me in the experience department - which is what counts. I'm more of a theoretical guy. Reality always seems to complicate theory, which proves theory does not take into count all the important variables.