The handle bar lever etc, would fit fine between the two bikes. The FJR has a clutch slave cylinder on the left side of the engine (directly across from the center of the clutch). I believe (not sure) it has a push rod that goes thru the motor and when activated, pushes out the clutch pressure plate releasing the clutch/friction plates.... The FZ on the other hand has the clutch release lever on the right side side, just above the clutch (lever operated). I don't know of any conversion kits.....
The hydralic system needs occasional service (flush/bleed) as well but gives a smoother feel than a cable system... Again,
in my opinion, there's nothing wrong/bad with a cable operated clutch, just a different system that needs more maintainance than a hydralic system....
I''ve been riding/working on motorcycles, dirt bikes/street bikes since 15 and am 51 now. I do most of my own wrenching on anything from a 125 2 stroke Yamaha,(70's) RD's, YZ's to my current FJR, KLR's(both 250 and 650), a Goldwing (04-sold), a couple of Harleys(sold) and several customers bikes, including a Concours, Suzuki B king, numerous BMW's, etc...
I had one bike, an 1980 Yamaha XS 650 (6k miles maybe, bought used) that tended to break clutch cables under the fuel tank, in the
middle of the center cable itself. It was not kinked/bent etc.... I don't know why the center (moving) cable would fail however it did, several times..... Try clutching with your left hand with a short piece of cable sticking out under the carbs.......

....
In
my experiance, lubing the clutch cable and throttle cables make them work easier and last longer.... The actual tool that I use is better than 30 years old, single screw clamp and was made by YAMAHA.....(casted/sold by Yamaha at that time)..... If someone has better luck without lubing it, excellent! Just trying to help out a fellow rider.....
Scott