B.Graham,
From the info, you supplied, your friend's gun is not Belgian at all, it is German. Gebr.Rempt Suhl( Rempt Brothers from Suhl)was a well known firm that made all types of hunting guns. REMO was their brand name. While not very legible, the proof marks are clearly German. Unless it has been rechambered, it is chambered for 65mm (2 1/2- 2 9/16") shells rather than the current standard 70mm( 2 3/4").
Mike