Gary,
I have worked on a varied number of gen and charging sets for the army, some dating from WW2, but have never come across this make before. I was dubious about it being ex-military, did a quick search and found a web site dedicated to engines and someone else was enquiring about how to repair one, they had a 34cc JAP engine apparantly. A poster came on to say they were used by the Royal Observer Corps at the underground posts for battery charging, he was a member so sounds like that is where they were used.
Site was www.internalfire.com