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Blocks are blocks. They're literally filler. Just about anything that bolts up and doesn't compress will work.
BUT, add-a-leaf springs are just $100-ish vs $20 or $30 for blocks. AALs add lift and reduce squat under load, and if you get full-length springs you won't impact ride quality.
Stay away from cheaply made eBay blocks. Took a chance on a set and this is what happened during the initial torque sequence of 110 lb/ft. Ended up going with a pair of fabricated lift blocks from Maxtrac with the built in bumpstops tangs.