Will a 1997 Dodge Ram pickup rear end fit 2003 1500?

No, a 1997 Dodge Ram pickup rear end will likely not fit a 2003 Dodge Ram 1500. While they're both Dodge Rams, the chassis and suspension were significantly redesigned between those model years. The mounting points, axle width, and possibly even the differential itself will be different, making it incompatible. You'd need a rear end from a 2002-2008 Ram 1500 for a proper fit.