Replying to Help me help my friend: px12 question

so my friend has a pair of px12 jibs mounted on some old armada arv's. he broke the brake off, including the plate, so they are dangerous to ride. i offered to replace the brake because i have a few extra of the right size. i just tried to do it, and the brake wouldn't fit. the bindings are pretty old, has the brake connection changed in the past? i have a pair from a few years ago and the brakes mount fine, yet i cant get them to connect to his. i try to put them on and push them back as far as i can, same as i normally do, yet they stop about 3mm from where they could be.

my friend needs these skis for next weekend so i need to do this soon. +k for helpful responses