I have a chart of the Harbour area which although not showing the pub ( it's a chart for those on the water ) shows the High Quay as one end of the "Mid Ferry " , or "Middle Ferry"
You may wish to search for that in case the Lord Nelson is on the photos
The 1897 OS map is available as a reproduction from Alan Godfrey Maps, and does show the PH on the High Quay. (They're available on Ebay and well worth adding to your family history projects! )
I went down that way this morning and the area appears to be closed off now , a few yards north of the High Quay / Quay Rd junction. However I know the guy who owns the security company who guard the area, I'll contact him to see if I can get access to check if any of the area remains from the "old days"