Some things I know, others not.

The company of Johann Sigott may have survived WWII, but is out of business now.
You can find some Johann Sigott guns and catalogs dated from the 1920s and 1930s via internet.
Here is an example: http://www.gebrauchtwaffen.at/item.php?id=2560
This gun is from 1925, completely reworked, with a new barrel or rifle barrel insert, but otherwise quite similar.

Proof marks are from the Ferlach proof house.
Böhler Blitz Stahl: barrel steel producer, good quality

All the numbers I can only guess:
698.37. should be the number given by the proof house; 37 may be the year 1937?
7.3 may be the groove diameter in mm
9.0 g (??) it may be the bullet weight in grams
MG Mantelgeschoss, jacketed bullet
1779 may be serial number given by gunmaker
all the numbers on the bottom rib ???????

I see no indication for the actual caliber, i.e. 7x57R or 7x65R or ......., sorry.

For any further information you might try the Ferlach proof house, phone +43 4227 2576

Fuhrmann