jlemon, I believe you're right regarding the Fort Worth Airport. Does any airline operate out of GSW now?
From the November 15th, 1970 OAG, I also found Eastern flying 727s into Titusville, Florida. I believe that airport is no longer serviced by any commercial airline.
WHBM, I did a little more checking in that November 1970 OAG. American's 707s are noted as either B3F for the 707-320 or B7F for the shorter -123s. The 720Bs are all listed as B2F. This is not to say that you're wrong in saying that AA operated its 720Bs on transcons, for perhaps they did at some point, but in that particular OAG there is no evidence of it.
As for the transcon routes that I did find operating with 720Bs, both were operated by Northwest:
JFK-SEA
IAD-SEA
Additionally WHBM, Thank You for the great detail on the early operators of the 707/DC-8. I never knew that Pan American had ever operated a DC-8-62. That's one photo I'm going to have to look for. I'm surprised Braniff didn't end up with it...