The only problem I can see is if you trim the blocks down to 6”, your outside strips will end up looking smaller than the inside ones because they are missing a full ¼ inch. How much smaller are they than 6.5? Are they off by just a little that you could make it up in the seams? Are they all off the same amount already? If they are all the same size already (just slightly smaller than 6.5), I would sew them as is personally.
Good luck!
Rachel