With a 73mm BB shell you have just enough space between the frame and BB cup to fit it (assuming truvativ GXP uses one 2.5mm spacer as per shimano?) This gives you no adjustment for the guide however. I’ve since tried spacing the chainguide piece from the backplate, but this will only help you if the chain happens to too far outward, which is unlikely
(I only have this problem because I’m using a 73mm octalink BB in a 68mm BB shell frame, so to account for this spacing the guide out 2.5mm from the backplate will put it in the proper position if I had a 73mm BB shell frame and had the XCR between frame and BB cup)
If you have a 68mm BB shell (if its a FSer, then its more unlikely) then you have 5mm space between BB cup and frame in which to mount the chainguide and the supplied spacers
EDIT: Just read the above post re: GXP, 73mm shell and no spacers.
Also just clicked on the link, I thought the XCR backplate was 2.5mm thick as per shimano BB spacers. They say they’re 2mm, which would give 0.5mm to play with positioning if it were replacing one spacer