Just picked up on this thread.
Some nice work there. I have a 4-4-0 director class that I built from a little engines kit many years ago. It has a rigid chassis is not a very good runner – derailments etc. I am probably going to need to build a new chassis so I will interested in following your build and seeing your thoughts on the use of the flex has I approach. I have been reading the Mike Sherman book. Quite a detailed study