I would guess Haid & Neu was the manufacturer.
The brass "Mercury" badge was probably the importer
The key unique elements that need to be accounted for are:
Two spool pins (usually on imports)
Two spool pins placed FAR apart. (unique)
The extra metal on the lower 4/5th of the serial number plate (most were simple flattened ovals)
Here are two examples off the top.
Here the one that is called "Faudels" (made by Haid & Neu)
http://www.sewmuse.co.uk/german%20se...chines%202.htm
Another Haid & Neu that is similar
https://www.pinterest.com/pin/408420259931796485/