I got frostbite reading this thread. What a way to welcome a newbe.
To the original question, a short answer. It has been reported from engineers that frequent this forum that the 3.5 is of a different architecture with many differences. As far as I know, no one has attempted to figure out the differences and see what it would take to stuff one under the hood of a Contour.
Now, if this same attitude would have prevailed when members were trying to figure out how to use a 3.0, that would have never happened, and they are very common now.
I think a 3.5 with its accompanying 6 speed trans would be a wonderful combination in a Contour, if it could be made to fit. It does look as though it will be a lot more work than a 3.0 conversion though. The details of the obsticles have been discussed every which way to the point that it is now nearly a bolt-in.
Wouldn't it be great if that is what ends up happening with the 3.5?
If you really do want to pursue this as a pioneer, start with a tape measure and see if the 3.5 indeed would fit in the same space. If old hot rodders were successful in mounting a chevy small block in an MG then what you want to do may not be impossible, but it may be impracticle and expensive.
Also remember the definition of a pioneer, the guy with arrows stuck in his back. A few such arrows were already launched earlier in this thread.