The left and right fiddle yard boards are now fully fitted with alignment dowels, and with only a couple of places where I've had to use some cereal packet card to even out the alignment:

Now, a couple of coincidental observations with regards to measurements, if you're into this sort of thing: the width of the minimum arrangement (as above) is 7 feet and a quarter inch. The outer circumference length of each of the old test track curves is four feet, eight and a half inches