Re: no reverse
Shift shaft spline is indexed incorrectly.
Drop the lower again, MANUALLY turn the splined shift shaft into Reverse gear, you will feel two index detents, one for Neutral, and one for Reverse.
Shift the throttle/Shift Control into Reverse.
Reinstall the lower unit again, taking care not to bump the shift spline hard enough to rotate it out of Reverse. Rotate the prop clockwise if required to index the drive shaft to the motor. Double check the water tube engagement as you come up.
Some chose to install in the Neutral detent and the Control Lever in Neutral, and rotate the flywheel as needed to index the drive shaft. Which ever works best for you.