My info comes from Cummins' own B-series shop manual. It says "Engine weight (with standard accessories): 6 cylinder engines ..... 410 to 440kg [910 to 970lbs]"
Perhaps "standard accessories" only means a water pump?
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1991 V1500 Blazer (Silverado), 5.9L 12V P-pumped Cummins (5x .012 sac injectors, #6 fuel plate, WH1C with external 38mm wastegate running 30psi), NV4500 with 1-⅜" input shaft, SBC Con-O clutch, NP205, HAD, 4.10 D61/14BFF spinning 37" Nitto Exo's
"I got a shotgun, a rifle, and a four wheel drive and a country boy can survive."