IIRC the Viscount 700s had hydraulic pumps on the outboard engines and the 800s had them on the inboards. Not sure if that affected the start sequence, but when taxiing in the 700s used 1 and 4 and the 800s used 2 and 3.
Electra (not British) always started no 4 first as that was the only engine with a 2 speed gearbox for the generator, so that all ground equipment could be removed, (GPU and air start), before up shifting to crossbleed start the other engines.