It may have been installed on an A4, but I assure you it's from a Speed. It didn't come on that A4. Here's a comparison from my A4 and my Speed:
As you can see, the Speed frame features the 3 pivot point holes for the trigger, which it inherited from the IR3, and has less milling on the trigger guard (and also on the back, but I didn't take a picture of that).
Wasn't being an *******, just thought you might like to know. No need to get your intestine in a knot
*edit* I only brought it up because i don't think it will be compatible with an A4, because of the vernier wheels.