426 Hemi

Back in the day, NHRA had restrictions on hood scoop size also for the cars. Looking at the pic the OP postedhis X-ram sits about 1/2-1in. above the hood line which means the carbs are at least 3-5ins. above that--too tall for NHRA (back then). The spacers allowed the motor sit further down into the chassis to alleviate that problem & maintain proper driveline alignment--remember engineplates were few & far between back than.
Nowadays builders put engines wherever thay want & build the driveline accordingly. For most guys trying to build a Hemi/A-body car they're best off not screwing with driveline alignment/phasing issues & just rely on how the factory did it. Any body, chassis, rollcage mods can be worked around the original engine location if they don't want to start from "square-one".......