Keep an eye out on craigslist for a used 26" kettle, and scavenge it for parts. As was mentioned above, it doesn't have to be a weber kettle, there are several knock off 26.5" kettles out there.
On cutting the top of the drum off, I wouldn't want to do that for myself. The better option would be to add a strip of flat bar stock to the inside of the drum that the kettle lid can sit on.
Modded Brinkmann Gourmet. Basic UDS. Rescued 22.5" OTS. SJS Mini-WSM. Stubbs. B&B Oak Lump.
Cannondale 2009 F8 (for burning off all the great BBQ)