Air bagging rear questions

[hanly2]

I am trying to plan my suspension. I have a short bed 1970 it has some lower springs and blocks on it now. I plan to bag it and I want to figure out how low I can get it while still using the stock trailing arm set up. I would like to be able to put the bags in the stock spring location. Can I use larger blocks to get lower without the arms hitting the frame? How big are the 2600 bags empty? I need to figure this out so I know how high I need to make my notch also. Also my frame is rusted where the 2 parts bolt together right by the upper shock mount in this picture. How hard is it going to be to fix that?
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