I did a OEM ZX-14 header install and built my own left mid-pipe/muffler mount. Worked out well but mucho work.
Delkevic makes a header/muffler system for your ZG-14. Don't have to buy one from a ZX-14 and adapt.
They offer the ZG-14 systems with 1 or 2 mufflers..
Several in the club has installed them and I've heard no bad reports.
I suggest that you get the bike flashed after install to complete the package.
Should get the HP up around 160 with a lot better torque curve..
https://delkevic.com/concours-14-gtr1400-1/?sort=featured&page=1Ride safe, Ted