@lewm,
The tonearm of the PL-70L II is very similar to the one on the P3 and P10, but not identical. The most obvious difference is that the P3/P10 arm is dynamically balanced, whereas the PL-70L II arm is statically balanced. The P3/P10 armlift also has its own lever on the armbase (instead of a push button on the plateau rim, like on the 70L).
It may have been available as a separate product, but I don't remember ever seeing it for sale. So it must have been quite rare, which would then go a long way to explain a $4k asking price.