Hey Pete,
I am doing almost the same thing except 350/350 w/8" and stock ford spindle/brakes. The stock spring was hung on the radius rods in front of the spring. Posies priced the spring for this at $190 for the spring over axle setup.
I plan on using the stock model A split wishbones. The axle was originally setup for cross steering. I haven't mocked it up to check on clearances, however I don't see how the tires would hit since the rods are at a greater angle to reach the frame. The tires are theoretically the same distance from the radius rods as the shorter axle.

Hope I helped you a little.

\Mike