Just a normal 20 spline tool and decent sized spanner.
@Chris S has obliquely pointed out that the drive side will have a left-hand (ie opposite to normal) thread.
Because there is not much interface between splines and the grooves, I suggest a 'cheap' tool is not a good shout: quite often a lot of moment is needed to start the unscrew.
How much torque to tighten in? 14" spanner, making sure the tool keeps engaged, and decently tight.