"...these cars can commonly vibrate when mount gets loose but not broken. Test is useful but does not necessarily mean everything. The pass side almost never broken externally but is in effect inside. It may look fine but be dead. ..."
"... Pull airbox and look for rubber crumblies all around the trans top mount, you can often see the top cross bar has separated from the rest of the mount...."
Almost never broken externally - and then you tell him to look for rubber crumblies and a separated crossbar? I think you need to reword that one.
By too light a body I mean too light a body compared to a slushmobile like a full size car or a van or a SUV. It's not too light of a body for what it is - an economy car that has some iterations with a sporty engine (the Zetec and Duratec) and a lot more interations with the throwaway engine (The SOHC) A smaller car is just plain noisier than a midsize or large car or van. That's part of the fun of driving them after all. The OP didn't say what he was comparing it to.
The thing is that your not saying exactly HOW to determine if a mount is "internally broken" So if the OP inspects all the mounts - and finds no physical evidence of breakage - and the "test for the motor jumping around" doesen't show anything wrong - then which mount is it? He's got no choice but to replace all 3 - and cross his fingers and hope that solves the problem. Well even if you go online your talking $150 at least for a set of 3 Ford mounts - thats an awful lot just to replace mounts that are still doing their job of holding the engine in the bay. $150 will get you a decent stereo that will drown out your low vibration. :-)