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**Bob B.** · 06-07-2020, 01:05 AM

Digging a little deeper I found in the parts text there are some differences between 'light duty' and 'medium duty' 350's. Unfortunately, it doesn't specifically say what the differences are, it just shows different part numbers. For instance, the light duty crank is a 3932444, medium duty is a 3941180. One is probably forged, the other is cast. The medium duty 350 has valve rotators, light duty does not. Blocks are different, medium duty is part #3961475, which could be a 4 bolt main. So, there is a difference.

06-07-2020, 01:05 AM	#6
Bob B. Senior Member Join Date: Aug 2005 Location: Los Angeles Posts: 1,309	Re: The "seldom seen" RPO thread Digging a little deeper I found in the parts text there are some differences between 'light duty' and 'medium duty' 350's. Unfortunately, it doesn't specifically say what the differences are, it just shows different part numbers. For instance, the light duty crank is a 3932444, medium duty is a 3941180. One is probably forged, the other is cast. The medium duty 350 has valve rotators, light duty does not. Blocks are different, medium duty is part #3961475, which could be a 4 bolt main. So, there is a difference. __________________ 1967 GMC CM-2500 Camper Cruiser, 351E V-6, NP 435 4 speed, Dana 60, and factory A/C. 2012 GMC K-3500 WT regular cab, 6.0L Vortec, 6L90.