Can't really answer the OPs q, but. Most Redmax stuff is like the other manufacturers. That is to say, mostly universal. Most 24xx series have a solid splined shaft as do most 26xx series. At least the S models that I've seen. The string trimmer gear box head will interchange with the edger gear box. I have switched them. The orientation hole in the outer aluminum shaft needs to be modified. But the shafts are the same.
I've also dealt with a couple extra shaky trimmers by simply turning the whole aluminum shaft around. Putting the gear box on the tranny end and vice versa. Switches the bearings in the shaft to the other end and viola! No charge rebuild. Of the handful of redmax trimmers I've had two that shook more than the rest. This little trick got both back in the race.