Anybody know what the stock shifter's height is? I think I might already have a short shifter installed on mine, but wanted to confirm.

 

It's probably pretty easy to check by just lifting the shfter cover and looking. I think "C's", B & M, GOTHAM and similar designs have a relatively straight shaft with little or no taper. PETTIT, MAZDASPEED, RX7store, MAZDATRIX designs have a short shaft above a very sharp taper. The stock shifter has a very smooth taper.
Mahjik's picture also had a ruler in it too. -----> https://www.rx7club.com/3rd-generation-specific-1993-2002-16/mazdaspeed-short-shifter-review-606860/