Hey Leonard; I'm not a big fan of the mono's, I've got a pair but not running them at this time. I can get it down almost as low with 3 leafs out of the original spring-pack. The ride is much softer (also have teflon lining between the leafs). The mono's get it down a little more but they ride like a lumber wagon!!
Posies makes a twin leaf lowering spring for trucks, I think Speedway has them. I hear they're pretty good but I'd experiment a little with your stock springs first.
Good luck with that beautiful '57.
