That is what I suspected. First, as somebody who worked with a tier one manufacturer of interior components for some time I can tell you that, aside from sound deadening, virtually everyone seriously overestimates what interior features weigh. Second, your argument has a problem anyway since the list you came up with is small at best and likely not entirely accurate. Examples.

I very seriously doubt the Ferrari has any more sound deadening material in it, more likely it has even less since it almost certainly utlizes a more expensive, more effective, and lighter material....likely a lot lighter than the 'Quiet blend' or similar material which the Mustang utilizes. Electronics and wiring.....were talking a set of electromagnetically controlled shocks and a few other handling gadgets to go with them. Since the Corvette apparently doesn't gain any significant weight buy using those same shocks I'm going to go out on a limb and say the Italian doesn't either. And there simply isn't enough of this stuff to make any serious difference even if it were heavier. As for carpeting, lambs wool is a bit heavy but 'cmon. You are grabbing at straws here.

No matter how you slice it giving the Mustang every last plausible item your argument could allude to you might see a 100lb gain, but I doubt it. This argument had never held up to scrutiny and it still doesn't.

 

I suppose the Ferrari's structure is made of billet aluminum then? IMO, a way to solve the weight mystery, unrealistic as it may be, would be a materials substitution and adding features found in the Ferrari to the Ford and then seeing how much weight would be gained. Not likely, is it?
By in-car electronics, I don't just mean the stuff that deals with the vehicle's dynamic performance, it also includes luxury items like power adjustable steering wheel, seating (motors), and sound/entertainment (amps, speakers...) system as well. I very well may be grasping at straws, but, as far as the carpeting goes - IIRC, Mazda did go that far to reduce weight in the last-gen RX-7 (FD) with lighter material.
Other than that, I wouldn't know where else to look other than the engine itself.