OK, Yes it is the diff and fuel tank from an R31 skyline but a sedan not a wagon but I am sure there is no difference in the 2.
Yes you could relocate the fuel filler but it was just ALLOT easier to run a short pipe from the origional fill point.
As for the angle of the diff/propshaft, they dont have to be parallel but you also dont want any HUGE angles. Just have a think of some of the 4WD's out there with massive lift kits in em and imagine what angles the propshafts are in them, some run double carden shafts to reduce the angle but its still pretty harsh.
![](http://datsun1200.com/uploads/smil49ca0afcd5bbb.gif)