Ash:
This is probably the GunBoards thread to which you refer.

There was a thread here on NE.com also that discussed the .577 x 2 3/4 in a Martini, jump to it here.
I have chambered the .577 x 2 3/4 "around the corner" into a .577/.450 chamber to prove the point, had some photos somewhere at the time but difficult to locate now.

Hope this helps.