I think it is a Steib S501... I had one on a RE Meteor in the 70's, hydraulic brake, was a bugger to match up to the crummy old enfielt rod brake, bur when done it worked a treat... and a fabulous outfit it was, had imense fun with it. I notice that the screen is missing and no sign of the hood or tonneau... i woild guess that it'll go for a fair few quid... even if it is a right hander... any bets.... i'm thinking £200 at least