I don't know Muir specifically, but if you guys are really staying with a 3-4 front then I can't imagine that ANYONE from the Colts defensive front would be a good fit. The Colts have been consistently bad against the run for years, and have nearly always had a heavy speed emphasis in their front line, with a lack of mass. This wouldn't be a good fit for the 3-4 front, unless Muir is the exception?! He measures at 6'2" and 320 lbs, so he's certainly not a massive DT.
Here's the report I got from The Sporting News.
Sat Jan 19, 2013 3:55 pm Chiefs signed DT Daniel Muir to a reserve/future contract.
Fantasy Source Spin: Muir's signing is the first of new GM John Dorsey's tenure. Muir played three games with the Jets in 2012 after spending four seasons with the Colts. The 29-year-old will be fighting for a backup job in training camp.