I bought a few bikes as a very ratty job lot years ago, found some had numbers filed off and other rather suspect things, wrote to DVLA with such details as could be discerned hoping they might be able to shed light on the identity and return anything to rightfull owners. They basically just returned the paperwork with an abrupt note saying they wouldn't supply a v5c without more details - as I was not that keen to invest in a cb250 superdream collection I took the parts I wanted- mostly a rear swing arm to replace one off my dad's old bike he had sold to a good friend that said friend had found rot in and done a perhaps not very pretty welding job. The rest was dispersed over the years and another friend did get one of them registered. However I wouldn't hesitate to just throw old frames in the weigh in pile. Several have gone that way here, used to be a good way to get spare tyres etc to buy a cat b salvage bike, they cut the headstock open to keep the bit with the number at the salvage yard, rest joins weigh in after being robbed of handy offcutd of tube.