I have a friend who races Miata's and sent this to me.
I haven't checked it out yet but want to share.

http://revlimiter.net/blog/2014/10/parts-review-miataroadster-short-shift-kit/

JV Sclafani
Boca Raton, FL
'13 M3W Metallic Orange Pearl
128CI Steered by Empire - Riding on Ohlins