I've also seen it suggested elsewhere that the French Air Force C-135FRs consist of 6 x 717-164 and 6 x 717-165.
I don't know if that's true, although if it is it could explain why they are serialled in two different FY63 batches: 470-475 and 735-740.
I've also seen it suggested that when the MD-95 became the 717-200, Boeing redesignated all the earlier C-135s as 739-1xx (as per the RC-135s), although again that's unconfirmed.