I have now added the Whale Experiment class:
(https://raw.github.com/jamespetts/simutrans-pak128.britain/master/trains/images/lnwr-experiment.png)
I think that it is just about distinguishable from the Prince of Wales class (graphically) if one looks closely enough. The Prince of Wales Class's tender will need modifying in order to connect to this.
The .dat file is here (https://raw.github.com/jamespetts/simutrans-pak128.britain/master/trains/lnwr-experiment.dat); translation texts follow:
LNWR-Experiment
LNWR "Experiment" Class 4-6-0