Hi all,
I happened to stumble across this thread and wanted to say that I built these Leach 2-way speakers while the original drivers were still available. I used the alternate 4ohm/8.2ohm resistor change for the tweeter attenuator. I have really enjoyed them. They are an excellent, fine sounding design. I liked them so much I bought Prof. Leach's book and have designed a couple other speakers using his recommended procedure.
Madisound sells the ScanSpeak Classic P17WJ00 6.5" Woofer that is supposed to be the equivalent, and unbelievably Parts-Express has the Goldwood GT-324 1" Titanium Dome Tweeter that is very close although the impedance is a little off. A $10 each, I might just have to buy a pair and swap out my Vifas for comparison.
Good luck.