Ihave fitted a VQ Statesman 80ltr tank to my VN Calais and the only problem
that I came up again'st was the Statesman tank straps were different.
I got the straps from a normal VN or VP Sedan with an 80ltr tank.
This was the only problem that I came across, every thing else went fine.
Good luck with the conversion and I hope that I have been of some help