Just changed the plugs (only plugs 3,4,5,6 before I ran out of time, see below) and wires (didn't remove the intake manifold), so now I can better judge these mounts.
With these SHOSource mounts there is definitely more vibration in the cabin. Most people would feel the vibration takes the car out of the "family sedan" category.
BTW, before changing the plugs I wanted to test the effect of changing the spark plug wires only without changing the plugs. I know, more time consumed, but hey, that's the price I'm willing to pay for the SHO community... Anyway, I installed the "Taylor Vertex '409' 10.4mm Pro Race Wires" I had bought from Vadim the Great many years ago, lost the wires but recently found. Wires are red with "Taylor '409' Spiro Pro Race Wire" printed on the wire. Not sure if they are the same as these wires from SHOSource:
http://www.shosource.com/catalog/product_info.php?products_id=282
These plug wires seat around the plug insulator much better than OEM wires. I can't imagine water or oil seeping past.
Well, with these wires my SHO is definitely smoother on acceleration, even with the new mounts. Throttle NOTICEABLY more responsive.
I was starting to do the plugs (Motorcraft double-platinum) and just finished the first plug, #3 when there was a hint of rain, so I quickly did plugs 4,5, & 6 before the rain started ( usually do all the back plugs first).
All plug gaps for removed plugs were about 0.048. With the new plugs I didn't notice an increase in power but the idle is smoother.
There was oil in plug wells 3 & 5, but not above the nut. Plugs were last changed 34,000 miles ago. I had replaced the plug well seals myself in April 2000, 75K miles ago (car was garaged most of the time I lived in Boston while I rode the subway).