I think Kevin nailed it. My car has similar links, and they are more than just traction bars. They are essentially suspension mounting points as the locate the axle, the spring and the shocks.

Dick, to answer your question, a fair number of cars in the SE Div run foam bushings on the top links, sphericals on the bottom and a tri-link. Others just run a panhard in addition to the stock four links.

I'm not aware of anyone replacing links entirely with homebrewed stuff, but I don't look under EVERY RX7 in the SEDiv. Just the ones that beat me......lol....seriously, it may be done, but this is the first I've heard of it and I've talked to a lot of folks here in the SEDiv with 1st Gen RX7s because your rear axle setup is nearly identical to mine.