Separate. 76T is former UAL metal. 756 is old CAL. CAL had the -400s; UAL didn't. The fleets are separate for now; will merge in a year or two.

In theory, if one got a 756 bid, one could find himself in a -400 occasionally...but I don't think it happens often. It pays more, so I think the -400 goes senior on monthly bidding/daily reserve pickup, and the 757 trips go junior.