A properly working pair of Rectilinear IIIs are levels better than the SP2000, imo.There are a few of these on ebay but zero any place I could listen before buying. These are top on my list I think unless someone thinks the Sansui SP2000 are a close second.
Here's a stereo review by Julian Hirsch from back in the day(vintage) where the IIIs were compared favorably with the renown Quad ESL 57.
I've also come to that conclusion based on the same comparison.
A properly functioning III Highboy is very hard to find fault but relatively easy to find, ymmv.
http://sportsbil.com/stereo/rectilinear-db/lowboy-review-hirsch-2-1972.pdf