I can't see this frame in the ledgers but in the engine book, it appears to have been an Irish conttact bike - despatched to Ministry of Defence, Dublin.
Which basically means that I don't have a clue. If it had been British War Office, I could have arrived at some conclusions from the serial number but an Irish bike despatched miles out of sequence, who knows ? Were they built and stored, built up from old parts or built to latest pattern ? I just don't know.
Are you able to find the Dublin registration for it ? Comparing Irish photos is going to be the only way forward here.