Here's two not been mentioned yet
Bobby Sheen Somehting new to do
Bettye Swann Kiss my love goodbye,
There's 100s more I could list but a lot might not fit other's ideal, suffice to say that I collected northern soul in the 70's and was sometimes swayed by hearing or reading about a tune and buying it, knowing it would never be played at Wigan but it was good soul all the same (Bettye Swann for instance),these are what I refer to in my opinion as crossover.