I'd say you have something aftermarket. RPO 254 as sstock mentioned was just an additional leaf, and not a two stage type. Your picture shows u-bolts that surround the axle, where 1/2 ton springs connect to the pivot just forward of the axle with square u-bolts.
Here's a page from the '52 Vehicle Information Kit that shows it as a standard semi-elliptical spring.
Kevin 1951 Chevy 3100 work truck Follow this saga in Project Journal Photos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together.
