Not so much build tolerances, selective fit coped with that, but manufacturing tolerances.
In "Not Much of an Engineer" by Stanley Hooker - highly recommended BTW, to anybody who hasn't read it - he says that Ford came to RR and said they couldn't make engines to RR tolerances.
He assumed RR were the bee's knees and the tolerances were too tight for Ford and was taken aback to find quite the opposite.
IIRC, he said it took Ford a year to redraw the Merlin to mass production tolerances, and then they came out like shelling peas as I mentioned earlier.