I would say Mayfair base with a Sheerline engine.
[Linked Image]
As CyberJack said muffler does appear to be on the wrong side.Much like the Sheerline has it on that side.Also the Sheerline emblem is on the front of the cowl.
So I agree it's a bitsa and has had an engine change.

Here for a good time,not a long time.