Is this the same as a 5100 LCF??? If so, just the cab and chassis will weigh 5,000 pounds. If it's the same as a 6100 (conventional cab) the cab and chassis will weigh about 5,300 pounds.
I'm not sure what the dump body will weigh, but think it would be in the 2,000 to 3,000 range. So the truck should ride on your 12,000# trailer just fine.
Mike B