I've ordered 4130 tube from
http://www.aircraftspruce.com/main.php
Your on the right track using 20mm axel hubs for the front. Take a look at the Organic Engines web sight
http://www.organicengines.com/Index.htm look at the photos for the take apart Troika,
http://www.organicengines.com/Troika...bits/index.htm
Its easy to use the hubs as single sided.
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Bentbaggerlen
"When the spirits are low, when the day appears dark, when work becomes monotonous, when hope hardly seems worth having, just mount a bicycle and go out for a spin down the road, without thought on anything but the ride you are taking." - Arthur Conan Doyle