Welding and regrind on the surface is a hit and miss, depending on the material structure and hardening, it can become too hard and fine structure with very little friction. Crimp on a sleeve is risky even if spot welded in place, it can crack or behave strange when red hot sometime down a steep hill.. Use the center only and weld on a new ring is maybe ok...in a pinch out somewhere on the russian tundra with no post office in sight... 

But there is good people that has devoted time, effort and money to research proper material, develop and produce precision press tools in order to make new, quality brake drums for us. Not only that but entire hubs and brakes sold separately and in parts.

The drum is sitting on splines, the same way as the sprocket on the other side is. And it can be drifted out with some caution. It can be difficult to remove caused by rust or slight deformation if the nut has been loose at some time. The drum and for that case the sprocket both on the hub and gearbox has to be fitted really snug, tap on fit. Any play will eventually work the nut loose, and if that happens it will not be pretty I'll tell you! Reject and return replacements that does not fit properly.

If you disassemble both sides of the hub, remember that the long portion of the hub is for the brake drum. It is sometimes found the wheel is turned the wrong way.

Rear wheel hubs came in at least 4 versions. Loose ball bearing hubs that has no humps. Timken taper bearing hubs with one hump or humps at both sides, and the -31 hub that is a complete different animal.

Front hubs came in 2 different versions. Small hump is for loose ball bearing and those with a big hump is for Timken taper bearings.