Nice report, Gordon. And well done with the anchoring and catch. It's not easy.
Regarding the confusion with tide and position of the wreck, you might want to try setting the GPS Map setup to "North Up" rather than "Track Up". I find this easier when trying to position myself over a wreck or other mark.
I drift over the wreck a few times with the track view showing on the GPS, and this will draw your drift lines (with North up). Then it's a simple cas of using the compass to point the boat back up the drift line and position the boat an appropriate distance from the wreck before dropping anchor.
See, easy!!!
cheers
BF