There is a screw on each side of the head that go into the aluminum block. They are directly across from each other just to hold plastic cover on.
Also noted that the alum block has a small centering pin on it for the short output shaft.
All of the bushings are .502 at max OD, but the widths area bit diff.
Output side:
Input side:
Input end:
As for input shaft it's solid rod so you could cut it down as much as wanted.
--Dan