For a bracket race type BB Mopar build, whatever real difference there might be in power wouldn’t be enough to turn me away from running the 150lb lighter block.  THIS! Whatever the power difference MAY be, it won't be enough to negate the weight loss advantage. The KB blocks are about 100 lbs lighter than a stock block and 150-175+ lbs lighter than a World block. Not to mention the aluminum block can be repaired pretty easily if you grenade it.
CHIP
'70 hemicuda, 575" Hemi, 727, Dana 60
'69 road runner, 440-6, 18 spline 4 speed, Dana 60
'71 Demon, 340, low gear 904, 8.75
'73 Chrysler New Yorker, 440, 727, 8.75
'90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt
'06 GMC 2500HD LBZ Duramax
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