Carl, you can try to find a model 1945 blackout mask, or modify a lorry one.
The lorry ones are Butler I believe, and are somewhat similar, but smaller in diameter.
Cheers,
Lex
email (option): welbike@sameagain.net
Even with that mod you won't see much in the dark. I have tried the experiment and it gets scary.
not so bad on a moonlit night but its the oncoming dazzle thats a problem,plus you'll not get seen.
remember that the original spec said the reflector had to be blacked as well.
Personally I'd say its a daft idea, probably illegal if you are in the Uk, but the experience of driving the bike into a ditch or another interesting but painful halt to your onward progress will provide an authentic experience.
But it'll look right.