Airgroup - my SLI mast foot looks similar and I have two "pins" going through the track holes that line up front and back of the mast foot and they hold the mast from moving aft or forward.
There are some pictures here in this thread, one pin is a cotter pin the other a SS bolt with a nut.
viewtopic.php?f=12&t=6033The thread is mostly about me trying to figure out the tabernacle set up on my boat but should help you.