I just had a go, and came up with something like:
Offence: 23 players
Defence: 21 players
So thats 47/53.
The last few guys:
Devin Moore (returner, backup RB)
Cody Glenn (perennial special teams star/ backup LB)
John Chick (DE who some felt was unlucky not to make the roster last year)
Rob Myers (thinking there has to be another TE, he seems like the only option)
Finally there will likely be a 4 way battle royale for the last couple of DB slots, between Cornelius Brown, Chip Vaughn, Mike Newton and Brandon King. They all played in games last year because of the colts ridiculous DB injuries.
Im interested to see where you guys think it will differ