Blind allen set screw M8x12, no matter what tip. Fit with low strength threadlock.
It's not an issue to remove the upper roller as it's totally useless. Suspension travel is not enough to allow the chain anywhere near the airbox or to increase slack to unhealthy amounts. On hard landings the chain hits the roller hard and sooner or later breaks it out of the frame.
I considered a modification with a support for the rollers shaft from the engine mount. Never made it as it's easier to just remove the roller all together.