What problem are you trying to solve with longer shock?
Do you really need taller shock or just stiffer?
Pre-gen is 440-lb/in, new-gen/300 is 475-lb/in.
The new-gen/300 shock is slightly longer at 320mm.
For bolt-on shocks, check out my thread with measurements here:
https://www.ninjette.org/forums/showthread.php?t=337292
Another bolt-on 320mm shock is this one (ignore photo, it actually has clevis lower mount:
https://www.progressivesuspension.co...shock-kawasaki
There is also SV650 and GSX-R shock retrofits, but requires machining of frame and shock to fit (in some cases, cutting fender & battery box). More involved that just swapping clevis on shock you already bought.