Hi Cynic,
Thanks for clearing that up. I'm away to have another trawl for more info. The frame number has mostly gone and I really can't make out anything. It looks like it could have been ground off at some point... The magneto flywheel on it is for a 50 and it's missing the magnets. There's a DT125 magneto on ebay, but it's possibly for a later model. Do you have any idea if they're interchangable? I suspect it's going to be a case of try it and see. ;)
Thanks again.