Pacers (14x), Sprinters (15x) and 170 Turbostars can all work in multiple with each other. GWR have run the 153+158 formation you speak of (not just Northern) as well as 143+153 combos, TfW (formerly ATW) have run both 150+158 and 150+153 combos and frequently run 142/143+150 combos as well as 143+142 combos, Northern have run 150+142, 144+142, 156+142 and even 158+142 combos as well as 155+153 combos (153s were converted from most of the 155s) and South Western Railway run 158+159 combos. ScotRail run or at least have run 158+170 combos, and West Midlands Railway (formerly London Midland) have run 153+170 combos for years and years. The classes can't be too "far apart" though; 150+170 combos (for example) can do passenger service, but 14x and 170 combos can only do ECS.
There are a couple of things to note: 1) if the train contains units of matching/mixed classes that are any of 150/2, 153, 155, 156, 158, 159, the train can be fully walked through, whereas if there are any units of classes 142, 143, 144, 150/0, 150/1 or 170 in the train, the train can't be fully walked through, and 2) in a train formed of units of different max speeds, the driver is responsible, when driving the train from a unit with a max speed higher than the unit with the lowest max speed, for not exceeding the max speed of the unit in the train with the lowest max speed (e.g. in a 153+158 combo driven from the 158, even though the 158 has a max speed of 90mph, the presence of the 153 in the train means that the train must not be driven faster than the max speed of the 153 which is 75mph). A 153 engine blew up in the past at 100mph, because a driver apparently didn't realise there was a 153 on the back of his 170!