cal trac question

Just found a add for what appears to be early cal trac 1 piece composite leaf springs for an a body.I never heard of these before anybody here have any experiance with these or what they might be if not cal tracs? Thanks

Landrum maybe?

I have seen Astro Van composite springs altered to fit in a race car with ladder bars.

Calvert originally used a 1-piece spring before switching to the 2-piece. Landrum sounds familiar as the manufacturer, but I'm not sure if they in fact were the source.
I assume the 2-piece deal makes it easier for them to supply different section lengths for different cars, as I don't see any other advantage to them over the 1-piece...