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It's more of a matter taste than anything. I like them as low as they will go reversed spring would be good. Are you going to run the spring in the stock location on a stock crossmemeber or something else? what about the attitude of the entire car what kind of tires and wheels are running a stock frame or Z'ing it etc. etc. The words Model "A" Roadster are like a blank canvas. Do some searches on pics and see if you can identify a particular look that your after then stay with the plan and go for that look.
I am confused are you going to use the I beam suspension or an IFS? Just my opinion but an IFS should only go on a car that has fenders, and unfortunatley Model A fenders won't hide an IFS suspension very well.