SOA (spring over axle) simlply means setting your stock leave springs on top of the axle. If someone talks of combining a "lift kit" with SOA then they are typically referring to replacing there stock springs with springs which have a greater arch and setting the new springs atop the axles. Of course you can also just buy lift springs and leave them underneath the axles.
Big 78 CJ5, 95 Chevy 2500 ext. cab
Big 78 CJ5, 95 Chevy 2500 ext. cab