if you can't sleep tonight - do a search on chamber length
you'll find enough to read to lull you to sleep
first of all- the only way to know the length of your chambers is to have them measured -
then you have to take your choice of the advice given in all those threads
some say stay short, stay safe
some say Parker meant the 2 5/8 chamber to use a 2 3/4 - the pressure spike may be minimal
some- i tend to one- will tell you to go light recoil loads because you are pounding 100 + year old wood- which loads happen to also mostly be the short, low pressure loads as well.
and yes - 2 1/2 in a 2 3/4 chamber will not be an issue