Engine prefix 950A identifies a 250cc 2T twin that was originally fitted to several makes in the late 50's. Ambassador, Cotton, Greeves Panther and Sun.
DOT never made a Villiers twin powered bike but one example is known to be built by an enthusiast, perhaps soeone else did so as well.
I haven't time at the moment to chase up the frame number but a photo would be of help.
Cheers,