A little late but this gets you GK3 on the JTV-89 the VERY hard way... still working great in mine though after what - 10 years?
search "HomeBrew GK3 into LIne 6 JTV-89" on the v-guitar forum or
https://www.vguitarforums.com/smf/index.php?topic=23087.msg167801#msg167801
of course when the Line6 electronics dies, it will be GK3 or analog guitar forever. Then again Line6 support of out of warranty JTVs is ??? anyway as far as I can tell.