A month later here is my follow up with pictures.
Using sash cord I hoisted a 12 foot beam, made of two 2x6's screwed together, up to the ridge board
I started with a single jacking point on top of the mid wall.
I soon realized the the beam would twist under load so added some plywood stays screwed to the rafters to hold the beam steady.
One jacking point eventually became six. Three points to jack and three points to bolster the beam.
I jacked the roof up to the point I was comfortable with.
I fastened 14 collar ties each 2x6x16'.
I removed the posts allowing the roof to settle.
The end result is the roof still has a bit of a sag but much less dramatic then it was. I would like to have gotten it perfectly straight but I am happy with the results considering. Total material cost was about $250.