Hmmm.... I would have been tempted to split the wishbone and use that entire axle assembly; it would be typical for the time period of the style car... Anyway, you will probably only need about 6 leaves in that spring, possibly less. Your car will weigh only about half what the '40 weighed and your center of gravity is back further. I would start by removing every-other leaf. If it's too soft or stiff when you're done, you can add or delete more until you get the ride you want.