I sold his big brother 350 back in the summer. It was a runner with MoT and Tax, new tyres etc but not restored,and got just shy of £5000 for it. The bloke said he was "more than happy" after he'd paid the cash over.
Good points for yours is that pre-war girder-rigids seem to be more sought-after than ever now, although being a 250 (in this age when 750s etc seem small) may reduce the appeal slightly.
Good bikes though.