Matt...I don't understand how you are able to jump to the firewall,
but I do agree that the connection to the engine is legal...try
looking at it this way.
Jeff - this jump comes from the lack of definition for how an engine stay rod is supposed to work. Allowing a transverse engine to hook to opposite sides of the car (left/right) is useless so is it safe to assume that the suspension stay rod definition is not in context here.

Allowing one engine stay rod w/o any definition on what that stay rod can or can't do makes it pretty free in my opinion.

I can run any muffler yes? Can I make it out of lead to add balast where I want it? Yes.

Is it pushing the rule a bit far? Hell yes. But I have not seen you leave much on the table when you drive the car so why would I expect you to do so when you build it?