were the ELGT wheels ever made in 18's?

Nope.

Were a 17' only iirc.

Originals were 17x8.5" champagne with champagne 'Ford' centre caps
Copies are 17x8" champagne or silver with silver 'Tickford' centre caps

Problem with originals on non-GT's is the GT's had a specially made steering arm and brake lines to suit the wide rims. This I imagine is why the copies are only 8" wide so you don't need those other modifications.

Uhh... No... Originals fit on my Ghia just fine.

You are thinking of the brake disc/caliper setup that needed a different upright, etc, to allow them to fit.

From: http://www.trueblueford.com/EL_GTspecs.html

I know there are differences, but not much.

GT's fit just fine. So says my car, the other Ghia in my driveway, and 3 mates I know with genuine GT's. I have no issues with contact with suspension components, body, etc, and neither have the other people driving around with them.

I am also to understand that all XR8's got a different steering rack with slightly different ratios to compensate for the extra weight over the front wheels.

The extra 1/2" of width seems to be in the outer dish of the wheel, as we all know there is a noticable difference between originals and copies...

But as I said before, you seem to be forgetting the GT's got different discs and calipers, which would have made different brake lines, etc necessary to make it all fit. Plus a wheel arch add-on which would make wheel arch clearances less than a standard EL. Plus GT's were running 245 width tires, compared to the 235's that 99% of everyone will run as 245 are hard and generally expensive to get.

I've known the true-blue ford website to be wrong at times as well.