A stock MX-5 front sway bar (from 2006 soft top in this case) fits on the rear of an S2000 with minor modification to the mounting brackets. The stock S2000 rear end links work as-is. This provides another tuning tool to balance handling front to rear. The stock 2003 S2000 rear bar is about 400 lbs/in and the MX-5 stock front bar is about 130 lbs/in.
Note that the FSB from the MX-5s with the metal roof are heavier (stiffer). I do not know how much.
Minor Mods
1. Elongate the mounting holes about 1/8" to allow the bar to move down and out of the way of the differential mounting studs/nuts.
2. Move the centering rings on the bar about 1/2" toward the center on each side. This can be done with a cresent wrench and a hammer.
Thanks to Dave Roberts and Mark Mays for the idea and proving that it can be done.