Reminiscent of a twin port JAP engine, but sadly without it's timing gear etc. This bike's been mocked up to sell it. The exhaust pipe, rear brake plate, 'bars, saddle mounting, engine plates and fork links haven't long been with the bike, though the forks didn't come with it either as they're too long, and the pitting on the front rim and frame members shows it's been outside in the weather for many years.
500 quid tops, and that's only as a long-term Thirties-style special build to the right person.