The P in the part number denotes a performance part rather than a replacement part, but the numbers are throwing me off. What do you mean by different arches like an SS? Oval track springs are arched, but are considerably flatter than even stock springs whereas an SS spring pack has a lot more arch to them than stock. If these are highly arched, then I'm at a loss.

Maybe they are old Walker Evans style off road racing springs? Might need someone with access to old performance parts catalogs from the early 90s/late 80s to help with P prefix truck part IDs.