Simon, Can you have a close look at the beams bolt to check they are Hex or Alan Key Head. If it is a hex head taking the track off will probably not help because the hole in the top of the beam will have top be to big and the beam would fail. In this case the bolt would have been held inside the beam with a spanner on a stick of some kind and tightened with the nut.
On the other hand if the Bolt head is an Alan Key head just drill a 7mm Dia hole through both the track and beam and undo it that way. This is the method we use on the new boats.
Peter