Thanks for the info, Alan.

If the last 1/3 was indeed by Arnold, and there's all the repeat stuff just before, then Walton must've basically just started it, reached a certain point, and then handed over. The thing is littered with Arnold's telltale brass glisses and run-ups, the sort of thing Rozsa was better at, Rozsa never took shortcuts in terms of thematic development to rachet up tension. Arnold would just run up a scale in crescendo.