Will a rear axle from a 98 silverado 1500 4wd bolt into an 03 silverado 1500 Rwd?

 

No. Your 1998 is an 8.5" rear diff with 5 lug axles, and your 2003 Silverado uses an 8.6" with 6 lug axles. It *might* bolt in place but you would need to check to see if the spring pads, shock mount locations, brake hose connection, and yoke on rear differential is the same and will accept the same U-joint. You WILL not be able to use the factory rims from the 03 on the back as they are 6 lug, and your 98 axle is 5 lug.