I was thinking about the wing, would it not just be cheaper to get one from a decomissioned plane rather than build a fake one from sratch?
I was thinking this as well, because when the plans were submitted the obviously had to have dimensions etc, and the only existing plane with these exact dimensions would be a 767, so they must have already picked up the wing.
The only other alternative would be they got a wing custom built, without the working mechanics, effectively a shell... A wing from an existing aircraft would be extremely heavy with all the mechanisms inside, and probably unable to hold its own weight too well, as featured in the plans (nothing is holding it up, it seems to be fixed at the base). So getting a custom wing built would weigh much less.
A new wing is about £4m - £5m brand new. And a wing off a decomissioned plane would still set them back probably up to half mill. (I study flight tech at uni, which is why I know this boring stuff) So I wouldnt be surprised if it was entirely custom built for them. and efeinitely will be a large part of the budget.