Thanks for the informative reply Rudy. I like the idea of wedging the braces in and am busily cutting oak wedges. Think these should be fastened into the mortice mechanically?

re: square rule V. scribe: interestingly, the original 18 X 22 granary frame was added on to some time around the turn of the century to double it's length. The new framing is, by your description, definitely square rule, as the joinery is just about all housed. The original granary has no housed joinery, but I have seen no roman numeral layout marks. I can still decipher, on some outside faces, line layouts on the beautifully smooth hewn surfaces. Wonder if these would tell me anything if carefully studied.
Another interesting thing about this barn is the way the addition was attached to the existing frame: Pieces I can best describe as bolsters turned vertically were nailed to the old posts. These are hewn 6X6 pieces, about 2 feet long, with a mortice to accept the new new plates and sheathing girts. The top and bottom are tapered to better accomodate nailing. Similar to the piece in Jack Sobon's scarf joint description in the latest guild journal (no. 60, p. 15 top photo right) but oriented vertically. Kind of funky but it's worked for the past hundred years or so..