Previous diaries had touched up on this subject
However, in researching the eligibility rules of the postseason, I came across this article
The important part is this:The pool of players eligible for the postseason is made up of the 25 players active on August 31, plus any players on the 15-day or 60-day DL on that date. Any of those players can be replaced by another player (who must have been in the organization on August 31) if the eligible player is injured at the time of the postseason series. Therefore, if a team has no players on the DL
on August 31, it has very little flexibility in choosing its postseason roster. Also, there was a rule change with the new CBA, whereby now teams can replace an injured player during the middle of a series.
So based on the above, it looks like we can substitute Dellucci for anyone (most likely Nixon) and we have one more free roster spot due to Snyder being on the DL.
I don't think it has to be position for position at this point.
Only if an injury occurs in the postseason would the substitute need to be pitcher for pitcher or hitter for hitter. Additionally, a team can now replace a player in the middle of a playoff series if he gets hurt and is certified by a doctor. This will prevent teams from having to play one or more players down if a guy gets seriously injured.
At least that's how I read it.