Art, the bolt and nut spreading idea will not work since you are pressing at the area where you also want to be removed (the axle flange).
Seeing what you have there now in the pic do you have access to two of the screw type jacks used on the newer cars?
I'd put one each behind the backing plate front and rear against the leaf spring and press it out that way.
If you have on old wheel laying around maybe bolt it to the axle and press on the back of the old wheel from the leaf springs.
Check your P/M...