Comment
It is certainly a good idea to fit one and I'm sure people did, but would the army have any kicking about they could use if most bikes just had an open bell mouth? They work on the same principle as a miners Davy lamp, the guazes stop the flame passing so won't ignite the fuel the other side.
It's got a larger diameter than the standard bell mouth and I'm sure the rivit counters wouldn't fit one 
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Henk sent me this picture. I guess also retro fitted. But at least sets a precedence to fit one. Ron
email (option): ronpier@talk21.com