I don't suppose anyone knows whether there are any books dedicated to the Class 03 and, especially, the 04 diesel shunter? I've had a look on amazon and ebay, and I can't see anything at all! There are a few odd books on diesel shunters in general, so they might be included in those. Maybe it's a bit niche?!!!
A few general shunter books, as mentioned above, the IRS 'BR diesels in Industry' being excellent for the movements of examples of both classes post BR use. Also 'The Allocation History of BR diesel shunters - 2nd edition' , a recent-ish reprint of the 'Harris' style volumes, and as with the IRS books, covers the history (in this case) of ALL shunters from class 01-14 and selected others. This is still available I believe, from the Heritage Shunters Trust web site for 22 of your finest British Pounds.
For books that lean more towards the photographic side, there are two volumes by Colin Marsden, 'The Diesel Shunter' and 'A Pictorial History of the diesel shunter', both OPC many years ago, although covering many classes the pics of 03/04 will be limited in number. Two more recent works with perhaps a few more images than the Marsden books, and in colour, are two volumes by Kevin Derrick (Strathwood), 'Looking back at Shunters 1 - The outside (ie non BR) manufacturers, including 04's, and 'Looking back at Shunters 2' which covered the BR designs, 03's included.
The Industrial Railway Society is a mine of information and various publications, which detail areas where both classes worked after BR finished with them, and a few works by Adrian Booth (amongst others) based on locations such as Manvers Main (NCB South Yorks Area) come highly recommended as histories of the areas/pits concerned and the locos that worked in same. The SY area of the NCB was probably the largest single user of (in particular) ex BR class 04's and most passed through Manvers Main in their time.