Update: This totally worked. I was concerned that the georeferencing wouldn't be right (i.e. that my lidar overlay would be in the wrong place) because key geographic features didn't appear to exactly
line up with underlying chart, but I finally got to use it this weekend, and it worked flawlessly. My depthfinder was reading 0.2ft at one point, which is probably within its margin of error, but I made it through without touching.
Thanks again for all your help!