Looks like WNG to me, maybe with added or updated parts. And the XG frame number would be right. So 1941.
If it was me I'd drop Bennet Longman a note with the pictures and ask him if he thinks that there would be problems dating it and getting a V5C from DVLA - he is the best man to ask.
Swindon Branch Secretary
Ariels - 1913 TT Model, 20 Roadster, 28 Model D, 30 Model B, 38 VH, 52 VH
The Offroad Fleet - Fantic 200, Bultaco Pursang, Beta Rev 3