It's not just the mounting ears, the bell is deeper, and the truck transmission has a longer input shaft. I think the front bearing on the trans is also larger, so the bell has a large opening (and bolt pattern).
Here's a note from John's site. First item on the list. Bottom line, if it going in a car, and you have a car transmission, you need that bellhousing.
http://www.ford-y-block.com/t5in-trucks.htm