Sorry for the delayed response. Steve's detailed information is of course very accurate and helpful, and I appreciate him stepping in to comment. We have been experimental partners for over 10 years, and by coincidence, have exactly the same technical training from the US Navy.
<<< In terms of optimal FSL signal gain and Q, what is the preferable ferrite rod size to use among the two Jaycar available options? Also, how are the number of Litz wire turns calculated to provide 520 to 1750 KHz coverage for a given number of rods? A new article would be instructive factoring in the more recently available rod dimensions, and improved lower resistance Litz wire. >>>
Like Steve says, the number of Litz wire turns for a new FSL design will always require some final adjustment, but if you have an existing FSL design covering the MW band with exactly the same components as the proposed design (same length and permeability of ferrite rods, same type of Litz wire and the same tuning capacitor), then you can calculate the number of required Litz wire turns prior to construction by using math, and usually be within one turn of the actual number. You accurately measure the coil diameter of the existing design, and write down the number of Litz wire turns in the existing design. Then you use the math formula where the length of one turn of wire is the coil diameter x Pi (3.141) and then multiply this by the number of turns, which gives you the total length of wire of the existing design. The total length of wire of the new design should be roughly the same, so you then use a proportion where this total length of wire is divided down by the product of the proposed coil diameter and Pi (3.141). This will give you a fairly accurate estimate of the required number of Litz wire turns in the new design. Like Steve says, with very expensive Litz wire it is a Cardinal Sin to cut an FSL coil too short, because splicing Litz wire degrades its performance. So the best option is to either play around with cheap wire as Steve suggests, or to cut an expensive Litz wire coil with an extra turn, in order to make sure that you don't end up with a coil that won't tune down to 530 kHz.
I'll try to answer your other questions later tonight, Todd. Good luck in your experimentation!