I got my antenna today and installed. I used the G37 Convertible antenna. I removed the circuit board from the FR-S antenna and placed it into the G37 base.
There are two places where you have to desolder. Both are shown below.
Next, pry open the metal prongs holding the antenna cable in place, shown bellow already pried open.
Remove the two pins from the plastic clip and take note of the antenna position in as shown below. The small one came out by tugging on it. The antenna wire you have to unclip from the front as well.
The FR-s circuit board fits into the G37 antenna as shown.
There are 2 places to solder to the G37 base. One is the previously unsoldered wire underneath the board. After doing this I placed some GOOP over it to hold it in place just in case. The other was also unsoldered previously in the second pic. The hole in the board actually aligns with a screw hole we won't be using so, I just dumped a lot of solder wire into the hole. This can be seen below. I also soldered another wire to where the original antenna mast touches and ran a wire through a hole I made on the plastic case.
Note, The oem FR-S nut can be used with the G37 antenna base, so that’s what I did.
Done. Thanks to Enigmus for the info.
The paint color doesn't match perfectly, but its barely noticeable.