No rivets, there's no way to get a press on the inside of the receiver where they go through. They're cap screws w/ permanent loctite, then the heads are filled, sanded and then painted (my little custom work ).
you can't put a screw on the side either to act as a safety stop due to the BHO lever on the inside of the receiver. There are some companies that weld a stud to the side, that's the only way I've seen it done.
Here's a pic of the rear receiver plate installed:
OK, let me clarify. The are two rivets (or pins) that run parallel to the axis pins through the receiver