The only remaining place to fit a larger chip is in the tender of the Britannia and Boadicea.

Here the tender has been separated from the loco. To do this you have to turn the loco and tender upside down and support it so that it cannot fall over sideways. Undo and remove both of the screws that hold the plastic base plate in position. Carefully lift off the plastic baseplate, and slide off the tender, and remove the 'bent' copper washer. Decide whether or not you want to remove the front bogies. They will probably have fallen off by now anyway.

Carefully. VERY carefully, replace the plastic baseplate (hole goes at the rear) and replace the screws.
These baseplates are over 40 years old. They are old plastic and can be brittle. They do not bend. Many of these have been broken by people taking short cuts and trying to uncouple the tendee or removing the front bogie by raising just one end of the baseplate. Don't do it -you will regret it, and spares are hard to come by. Any unti that is 'sold for spares', more than likely will have its baseplate damaged.