Emmet:

You are correct in assuming that the tenon will need to be cut. That would be singular becuase the north end is just a butt end seated in a housing on a 6x9 repair post and held in with more masses of iron rod. The ends will be supported by a mechanicaly fastened (with wooden plugs to cover offending hardware) bolster or ship's knee if I can come up with one. Should I need to use the bolster I will make up new braces at new angles and retrofit with wedged hardwood to foot the braces. Admittedly I am hoping to find some knee stock as that would be much nicer in the shop environment (and a lot more interesting).

As for the other tie beams, my plan is to use an idea I got from Herr Brungraber - Simpson Tension Ties on blocking that would get them to the appropriate heihgt. Fortunately they will then dissapear as the walls go up. I don't like all this metal stuff - wood is nicer - but sometimes you have to adapt to the situation at hand.