Froze, 1985-1986 sounds about right for the LePree. However, there were both 2 and 3 pulley versions available at the same time. Nishiki's exclusive, one year deal was only for the 3 pulley version. SunTour also offered three pulley versions of other derailleurs beside the LePree.
The SunTour bottom brackets and cranksets were likely made by Sugino. SunTour, Dia-Compe and Sugino were all part the JEX association of Japanese manufacturers who had a non-competition clause with fellow members. So, when SunTour wanted to market a group against Shimano they had to go to JEX associates like Dia-Compe and Sugino for the brakes and crankests. However, we cannot rule out Takagi, who was another JEX crankset manufacturer.
As for the lighest derailleur, Bicycling lists the mid-1980s Cyclone MkII rear derailleur at 161g.
However, there is no denying that, in general, SunTour derailleurs offered excellent performance and value, across the line. At least until SunTour's slant parallelogram patent expired and Shimano was able to incorporate it with their SIS indexed shifting system.