Yes to all of the above, except the head. Your TW head will work but you might consider the 225 crank while you're at it. It's the same amount of work to take it out to 223 since you'll need to split the cases to open the case mouth.
XT's and TTR's are 70x58.
TW's are 67x55.7.
223cc with the crank, 214cc without.