Sounds like it’s Junkers then, probably an 88.
Have a look at the Norwegian Ju88 restoration site of the one that was raised a year or 2 ago. Loads of pics there, no link at hand sorry:)

Have cleaned away some more silt. The locks have a brass casting. There are the following numbers on these castings- read a previous thread about numbers on castings and found

1R 3115

and

Ju N 16410

Also saw some Ju 88 wreckage photos on ebay and there was an item identical to the triangular swivel mount amongst them.

Any Junkers expert who can put this to bed for me?