Nothing wrong with using flat leafs for the SOA (as long as they aren't falling apart due to rust). The original leafs I went with pretty much shot (actually, they were very shot), but with the addition of the MJ main AAL, they've held up fine and have given me several years of problem-free wheeling. I'm only replacing them due to rampant rust that is weakening them (don't really want to experience a break on the trail far from home). The replacements are 2wd MJ leafs with an Explorer main as the AAL. I can tell that I've got a couple inches of lift over the old set, but the truck isn't at full ride weight so I'm ignoring it for now.