Glez is quite correct - although I disagree with the "Some cosmetic work was done in the front spoiler." - it was a bit more than that - the front end is completely different. It's often referred to as a 348 front end - which is a fair description, as they're extremely similar.
You'll find all the differences outlined on the following site:
www.red-headed.com
The 512tr is meant to be a considerable improvement over the Testarossa - although only having driven a Testarossa I can't confirm that. If it's true, however, it must be spectacularly good.
Bazil