I know exactly what you're talking about. I have one of those sitting in my side yard. I got the tranny, ran the tags on a T5 search (the site was
www.5speeds.com, on the side bar go to T5 5 speeds, bottom of new page, tag searcher), same thing, 1984 5.0 Mustang/Capri. My tag numbers were 1352-065909 and 1352-066923. It looks like a T5, but there are differences. First, the shifter opening is much smaller, that's how I first realized it wasn't the right one. My aftermarket shifter base was way too big for to opening. Second, my bellhousing I got from an 88 5.0 wouldn't fit on the tranny. The four bolts were in different places and wouldn't match up. But it is indeed a 5 speed, with a rod I shifted and counted 5 gears and a reverse. Go figure?!?!?
BTW, I have a picture of it. If somebody can tell me how to put a picture in my post, I'd be happy to put it up.