mod requirements at a basic level for when I did my VTX 1300 also I did this after my HD control mod since that didn't work so good with the caliper being to firm this allowed me to keep the stock VTX brake master cylinder which provide less deadly brake feel
1. new throttle cables from barret get the ones that are harley to honda
2. some HD style throttle housing (I used Joker Machine but there are tons like Performance machine, bitwell, arlen ness, etc)
3. HD grips / throttle sleeve
4. Lots of good connectors not like the ones they provide
5 grip ace system
6. on/off switch (I used Joker machine to match the throttle housing but again tons out there)
Also Excile does do a lot of internal wire stuff but it also depends on the year HD that came from if it is throttle by wire it would be different than throttle cables! You could contact Russell Mitchel of Excile about the cable length but don't forget those are custom bars and your bars do not have a recess for the grip ace system so putting it under the grip was the best option.
Also Excile or Grip ace can customize metal grips to fit the system which is really nice. I am cheap so powder coating and rubber grips for me!
Greg
Owns
2000 HD electra glide
2005 HD Road King
2006 Honda VTX 1300 C (first love)