The last proper steel sliding sunroof was the XA-XB Futura/ XC item.
After that, the power moon roof option was an LTD option form the first square Fairlanes and LTD's. I'm not sure about when the sliding steel roof arrived. All XD-XE-XF's missed out on that unless I'm mistaken.
If you've seen a sliding steel item, I'd say its ex LTD/Fairlane. Some people do LTD/Fairmonts roof swaps on Wagons and sedans. I've seen only one steel slide sunroof, in a Aussie Ford Performance mag. It was a dark brown or black, had a 460, XD body with XF front, LTD roof and sliding steel sunroof, plus a boxed in C-pillar.