Wow Eric, that bottom looks great, nice job.
Mark the coupler between the shaft and the transmission with white paint. A line fore/aft on top of the coupler when the prop is vertical, two lines for either blade up.
Here's the big tip. You can see the coupler if you take the bottom out of the top step (use a flashlight). Make a little tool to turn the engine over using the pin in the middle of the flywheel (the thing you would use to manually start the A4). The tool I have is a couple of pieces of (3/4" ?)pipe connected with a 90 degree elbow. Use a hacksaw to cut a couple of notches in the end of one of the pipes. Now you can leave the engine in gear, look over the top of the engine at the coupler, turn the engine over by hand until the white line is on top. Prop centered. (really helps with the folding prop)