You should stick to light loads with your Flues model Ithaca:
Polywad 'Vintager' http://www.polywad-shotgun-shells.com
Eley subsonic/low recoil http://eleyshotshells.com
ARMUSA 'Vintage' http://www.armusa-performance.com
Kent http://www.firearmservice.com
RST
http://www.rstshells.com[/URL] 570-553-1651

As has been discussed several times, shooting 2 3/4" shells in 2 9/16" chambers increases pressures little (not more than an additional 300 PSI) BUT pressure and recoil are not the same thing. You still have a gun with 80 year old wood and shooting light loads would seem reasonable. I think you've already reviewed this thread over on 16ga.com http://www.16ga.com/forum/viewtopic.php?t=1694