TWA had 707-131 ( the 31 part was the number assigned to TWA by Boeing .) This plane was a non fan engine with water injection.
Then there was the 707-331 - a larger 707 non fan plane.
Next was the 707-131B - a true rocket ship. Small 707 with fan engines. A real trip to fly!  :-*
And then the last of the group was the 707-331B series. This included the 707-331BA, BAH and C versions. All had the larger fan engine with various leading edge flap differences and higher take off & landing weights. The BA & BAH were similar, but the H stood for heavy - it had stronger landing gear.

A side note, the 727-200 was just a few inches longer than the 707-131B. There were always the pilots that said they flew the "big" Boeing - meaning the 707, but when the 727-200 came along they had to shut-up!  ;D  Of course the 747 ended all that BS.  :P

Lou