At last, the White Rabbit (IV) and the Dormouse sit side by side or nose to nose in ridable condition. The TT bike "White Rabbit" is in its 4 version because a. I'm not very good with pure TT bars, b. The land here does not have enough flat and traffic free roads for me to train and c because I'm not very good with pure TT bars. This is the short extension version with drop bars for its ability to climb.
The MTB "Dormouse" is the current dirt "road" bike intended for general use and to be my usual training bike. The pictures show a similarity in the fork angles and trail. This results in handling remarkably similar to the Rabbit and was the principal design requirement for the training mule. The bars are just a smidge taller as comfort on dirt for longer distances seems to require a more upright position. As with BluesDawg's current conversion, drop bars may yet be installed. They will be at the slightly higher height also to maintain the legs to chest angles as on the TT bike.
It has been fun to build a pair at a time to see if one rider could be happy with either on a moments notice without a lot of change.