Don't worry about the Fore and Aft movement. That is designed-in. Each hull flexes and shrinks differently during the molding process, storage and shipping. Perhaps even with tying down for roof top transportation. The drive must seat under the cams and is allowed a bit of fore and aft movement so those two spots as fully seated first. Some boats will be tight, other may be loose. When the drive is in use the system rocks forward and that is it. Some people have added a spacer up front, but it isn't critical.
Go ahead and mail in the sheet for the cassette well plug. We may end up having to ship twice, but don't worry about it. Harder to manage than it is likely worth.
Director of Parts and Accessory Sales
Warranty and Technical Support
Hobie Cat USA