596 heads spring installed height too low

Your best option is to use Crower 68405 springs. These are for FT cams, about 130 lb @ 1.650" ht. Pontiacs have a low installed ht, & the 68404 & 68405 are used a lot on those engines.
From memory the 282S cam has 236* @050, so is going to want about 130 lb on the seat.