Thanks Daiku...but we have two interior walls that go down the middle of beams and posts(so the timbers show from both sides)......the drywall will butt up to the beam and that is what we are trying to finish?..ideas?

PS On the outside walls we also spaced the SIPs out to slide the drywall behind...That is part of why we thought the gap would look fine.. A 1/8th inch shadow line just like the one by the wall.