This video documents a tour given of Class 28, D5705, which is undergoing a long-term restoration:
https://www.youtube.com/watch?v=IIYnD7uQGho

This is an example of how a tour, similar to a "hard hat" tour on a preserved ship could be conducted on carbody locomotive that might be out of service or undergoing restoration.

This locomotive has been undergoing an extended restoration an extensive multi-year restoration led by the Class 15 preservation society. More information on the restoration effort may be found here: http://d8233.org.uk/