Here you have XPacks I used for my GB Sprint stage. Textures for roads, roadsides and terrain were taken from original RBR tracks and packed into XPack (WB Roads...).
The second one is an XPack made by jay_666, but optimised by me. The advantage of mine is that it uses much less resources on final track. The XPack contains tons of objects and vegetation from various original RBR tracks, including Great Britain, France, Japan and I think some USA.
https://www.sendspace.com/file/u666qv
Warning - if you already have used jay's XPack, called "Great Britain (RBR).zip", don't use mine, because you would have many materials and textures doubled in your project.
You can also create your own XPack with other RBR textures - just open some .rbz file with 7zip or Windows Commander, load textures (usually TrackTexturePlateOpaque.dds and others) to Photoshop or Gimp and cut all texture parts you need. Save as single textures and make XPacx(s).
This is my GB Sprint track after conversion to original format:
Unfortunately, I think I lost BTB version of that track...
I hope this helps
M.