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I am curious what your research turned up.
My impression is that that the second pair of shocks was to dampen rear end rotational hopping during launches. The short, angled upper control arms were intended to limit torsional movement as well as lateral movement of the rear end housing. This was supposed to eliminate the need for a panhard bar or Watts linkage. The arms were so short and the mountings so rubbery that they limited neither movement very weel.
The reason nobody uses the quad shocks is because they usually improve the rear end mounting design by improving the angle of the upper control arms (closer to parallel) and adding a panhard bar.
Brian
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