Um... I would sure hope so since they are both 2003. But if you mean "will a bumper from a 03 silverado 1500 fit a 03 silverado 2500, (or the other way around)" I am not sure. It might, but the frame on the 2500 is bigger than that on a 1500.
Will a 2000 chevy 2500 bumper fit a 2005 chevy 2500
It should, but the upper bumper pad on the 2500 may be thicker, they both bolt on the same way though, measure the height.
The parts should fit.
YES
No totally different style
No, Chevy changed the wiring harness in 2003. and the way it is mounted, it can be made to work though.
it should. the only thing is if one was a diesel. sometimes they have a spacer on the diesel models.
A eaton fuller 18 speed roadranger gearbox is used
NO
YES, They will fit with no problems.
Yes.
YES.