Phil,
I had the same issue. Having already built the wings I modifed cabin top to fit. Also page 32 the plans shows the bottom of the tank at 28 1/2 inches long. If the cabin top was at 29.8 the tank would not sit on the top tubes.
Oh and... The template for the wing ribs pretty much dictates where the spars go, leaving moving the fuselage the only place you can make a change...
This was just my interpretation, YMMV.
...Paul