I installed some Grover 406c locking tuners and a GFX X-Trem tremolo on my JTV-59.
Special thanks to Christian at www.townerusa.com for selling me his Bigsby V.Block spacer and straplock extender, which was needed to move the X-Trem back from the bridge...
The V.Block fit perfectly, but the straplock extender was just a bit too long to fit inside the X-Trem so I used a dremel tool to lengthen the staplock hole on the X-Trem.