Originally Posted by
fietsbob
a strip of aluminum 1/8"Thk x 3/4" wide, and drilling some (4) bolt holes and threading them,
will give you a way to Mount your water-bottle cage
at a different height than the factory installed Bosses allow.
+ twofish.biz makes their velcro and rubber block mounted cages to fit Larger volume Kleen Canteen Bottles
Twofish Vinyl-Coated Quick Cages - Twofish Unlimited.
And Bladder bags in your panniers and a smaller bottles handy can combine to make Nevada Crossings hydrated.
Yeah, should be easy enough to rig an adapter with a strip of 6061 aluminum, if you're set on making dual 40oz bottles work.
Two standard large bike bottles and a flexible bladder bag or two is IMO the more sensible way to go. BITD we used to carry a couple Bota bags for that.