I understand the engine will run as it should and will not overheat because of just this sender, as it's only connected to the gauge. But it is not how it should be, and like YBJ I would like to have the correct sender in there. If that sender is no longer available I can understand that this could be the best alternative. But according to YBJ the correct sender should be available and in that case it is simply a case of supplying an incorrect sender.
You could say I shouldn't make a point out of this. But I have another Sierra on which the gauge sits as how it's supposed to be. And every time I drive the cosworth and look at the gauge my first thought is that it is going to overheat, which is really annoying.