Originally Posted by
Retro Grouch
AHA! You're missing a piece - 4 pieces actually.
There is a stud, that isn't normally supplied with the brake, that threads into your frame mounts. They aren't too expensive but you probably need to take your bike frame to the LBS when you order them (they'll almost surely be a special order item) because there are different sizes and threads. Once you have the parts, I think everything else will make a lot more sense.
Good eye RG.
I missed the brake post not being there due to the angle of the pic, thought I was looking at the end of it.
It could very well be that they are still on the brakes that were removed from the frame. Sometimes the bolts seize in the post and they come off even though they're meant to stay with the frame. If that's the way the frame came you should find an overflowing drawer of them at almost any LBS.