I bit the bullet and ordered a ready-made KX1688.
I have wasted that much already on the dead ones.The ferrite coil connections were revised and agree with the diagram. It irritates me why I never heard a peep from any of the four I built. Why wouldn't the local osc run
I extracted the 9018H that was the mixer osc & tested it. It has a hfe of 115, which is close to the figure for other spare examples I tested. By contrast a 2N3904 gave an hfe of 321
It made me wonder about using one in the sole IF amplifier stage of an example of the six transistor kit type HX-6B or as the mixer/osc.
BTW: I just got a near-new Antex XS25 soldering iron, so I can't blame my tools in future.