The acquisition or hiring of various redundant track machinery is an important aspect of the many heritage lines around the country. It helps with the maintenance of their tracks and when extensions or remodelling is being undertaken. DR73307 is a Plasser & Theurer 07-275 T tamper that has recently arrived on the line presumably in association with their work extending the line south towards their new station at Boughton, see....
https://www.nlr.org.uk/boughton-extension/