Shaun
I don't know what size your posts are, but is it possible you could hold your posts in to allow the SIPs to land on the foundation?
The area of post landing on the wall may be enough to carry the load and if not, (check w/an engineer) perhaps with the help of the afore mentioned angle iron either at the top of wall or lower with the post notched to reach it. If this necessitates you could add sill to the inside of the wall by drilling anchors where needed (not as time consuming as it sounds). Nothing like changing the plan eh?
