The FLSun SR is a great machine for the price, and it is a good base to improve upon. As soon as I got one I decided to go direct drive (well, remote direct in order to leave the effector as light as possible). I removed everything from the original effector and I designed a simple mount for the Zesty Nimble, that I printed in polycarbonate so it could withstand high temperature. I had to file the aluminium effector a bit or the Nova hotend (that is asymmetric on both X and Y) would have touched the metal transmitting the heat. I used Orecus' 5015 blower fan adapter and I modified Diabolikal's fan duct as the Nova is shorter than the Volcano hotend (both on Thingiverse). Since the Nimble has a 30:1 gear ratio, I designed a "speedbox" (1:3.5) inspired by BunnyScience extruder motor gearbox in order to allow faster retractions/speed, also because I'm using a 0.9 degrees stepper motor.
Finally, I installed Klipper so I could have Input Shaping to allow nice and clean prints :)
In the video I am printing with the Nova default 0.5mm nozzle, at 0.3mm layer height and 100/140 mm/s speed for external/internal perimeters. Accelerations are low in this case, at 5K for infill and 3K for perimeters/surfaces. My draft mode is at 7K for infill and 5K for perimeters/surfaces and 120/180 speed.
The Nova hotend can easily print at 35+ mm3/s.

Links:
Orecus 5015 blower fan adapter:
https://www.thingiverse.com/thing:4917075

Diabolikal fan duct:
https://www.thingiverse.com/thing:4899374

BunnyScience gear box:
https://www.thingiverse.com/thing:3553286

3D Passion Nova Hotend:
https://3dpassion.com/nova

Zesty Nimble Flex:
https://zesty.tech/

Here some photos of prints done after the mod (with finer layer height!):
https://photos.app.goo.gl/hBFyd9oB97Nztn8j9