Good project, hope you'll post photos as you go along. There is a pretty comprehensive guide here on Sheldon Brown's site: sheldonbrown.com/tandem-build - sorry, I've not posted enough to include the full url but this should get you there.
William.
Think i might be changing my mind as i learn more. LOL. There are evidently zero single seat touring bikes for sale in Phnom Penh bike shops let alone tandem tourers, and my girlfriend says she's not comfortable riding her own bike on the mad roads so just weighing up my options and also find this stuff interesting. The satisfaction of touring through countries on your own built frame!
As far as the tricky frame alignment go's for complete amateur builders - would lugged joints make it possible to get away without using a jig and enable you to align by eye and straight edges, plumb lines etc? Are the lug joints tight enough on the tubes to allow very little movement?
Say for example you used lugs on the most important alignment points of the frame, assembled the frame, aligned it by eye and string (without a jig) , and just made tiny removable tack welds on the lugs and then checked the alignment?
#PossiblyDreamin'