the manley rod is .050 narrower than typical BBC rods (like the 6.7 mostly used in BBF builds) that is the difference in weight your seeing
the horespower rating is affected by piston weight and rod angle, longer stroke........... wider angle
IMO the scat "pro comp" rod (about $300.00 per set) would be a good value along the lines your thinking, however, it is heavier see specs below
Manufacturer: Scat
Mfg part #: 2-ICR6700-7/16
Description:
• NEW Forged High Tensile 4340 Chromoly Steel
• 7/16" ARP/Scat 8740 Cap Screw
• Lightweight "I" Beam construction
• Each forging is x-rayed, sonic tested & magnafluxed
• Shot peened to stress relieve surfaces
• Packaged in weight matched sets ± 1 grams
• Big block rated to 800 HP
the horespower rating is affected by piston weight and rod angle, longer stroke........... wider angle
IMO the scat "pro comp" rod (about $300.00 per set) would be a good value along the lines your thinking, however, it is heavier see specs below
Manufacturer: Scat
Mfg part #: 2-ICR6700-7/16
Description:
• NEW Forged High Tensile 4340 Chromoly Steel
• 7/16" ARP/Scat 8740 Cap Screw
• Lightweight "I" Beam construction
• Each forging is x-rayed, sonic tested & magnafluxed
• Shot peened to stress relieve surfaces
• Packaged in weight matched sets ± 1 grams
• Big block rated to 800 HP