Right after the assembly, a basic test confirms the modules work, though the pulse generator frequency is somewhat off. Replacing a 6.8 kΩ resistor with a 4.7 kΩ should fix this.

When one module is fed with the 1 kHz signal (from the oscilloscope reference generator), the other receives the signal with a slight delay (as expected).

Funny that the practical formula for the pulse generator frequency is f = 1 / (3.14 * R * C), not f = 1 / (2.197 * R * C), as advertised in the source. Some early π-day interference here!