Expanded metal ring in a 22" for short cooks. Its about the size of an SJS charcoal grate.
One I made that's smaller than an 18" WSM ring in a 22".
Inside a Cajun Bandit ring.
Another made of perf steel @ the size on an 18" WSM ring.
I use smaller dia. expanded metal rings in my drums, and figure I get over 5 hours of burn time from a Weber chimneys worth of Kingsford briqs, (@5lbs) cooking direct. Never paid any attention to cook times indirect, but I never add fuel during a cook either.
Absolutely no reason it wouldn't work in the 26.75", I never have, but did modify some charcoal rails to replace the puny Char-Baskets.
Go for it!