OK, they're NOT for the same "application". I looked up drums for my truck, which happens to be a '97 K2500 pickup, 8600 GVW, with the 10.5" ring gear, full-float axle:
The '0363: Rear; w/ 8,600 lb. GVW; w/ Full-Floating Axle; w/ 5.1" Drum Height
The '0449: Rear; w/ 8,600 lb. GVW; w/o Full-Floating Axle; w/ 6.51" Drum Height
So the '0449 is for the semi-float, and the '0363 is for the full-float axle. Full-float axles have the drums on the back-side of the hub flange, closer to the backing plate. The drum can be shallower. The semi-float axle has the drum on the outside of the axle shaft flange, farther from the backing plate. Drum needs to be deeper.
The '0363: Rear; w/ 8,600 lb. GVW; w/ Full-Floating Axle; w/ 5.1" Drum Height
The '0449: Rear; w/ 8,600 lb. GVW; w/o Full-Floating Axle; w/ 6.51" Drum Height
So the '0449 is for the semi-float, and the '0363 is for the full-float axle. Full-float axles have the drums on the back-side of the hub flange, closer to the backing plate. The drum can be shallower. The semi-float axle has the drum on the outside of the axle shaft flange, farther from the backing plate. Drum needs to be deeper.
