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The look more like stock runners that have been reworked and siamesed (look at the holes between the runners that are now opened as a single passage). Then the top side has been cut out and new material welded over the runners to open up the inside.
Seen the ad for those myself, think it says they are custom, so I'd assume stock moded runners. Think they are siameases too far, was thinking bout modding my stock and rem reading it's better to keep it bout the same as slp or the as&m. Decided it's not worth my time becuase I'd still have small tubes.