Tankers - 767 or 7E7?

I have been wondering why the Air Force doesn't look to buy tanker versions
of the 7E7, rather than 767s? From what I've read, the discounted price of
a 7E7 to the airlines will be under $100 million, possibly well under. So a
100 of them would cost less than the $10 billion being cited as the price
for 100 767s. As a launch, and substantial, customer - the Air Force might
be able to get a goodly discount, as well as some say in design (like maybe
alternate rack designs to hold Mil Std avionics). And the tanker versions
should be even cheaper because they wouldn't need airline features like a
complex galley, multiple lavatories, and entertainment piped to 250 seats.

Better yet - why not procure some of each? There have been statements that
there is a risk in having all the tankers be of one design in case that
design is grounded for some reason.

You know that whatever the Air Force buys will be flying for 40+ years - why
not get the latest, most efficient, and lowest maintenance aircraft?

Tony (first time poster)