It sounds feasable. One thing is that I would consider is using some cross bracing once the barn is straight. Its nice to see someone trying to preserve their barn. around where i am most people just tear them down and start over. Best of luck!

I have a 30 x 60 foot barn with a slight list in two directions. The lower plate in the SE corner is gone 10 feet in each direction. I plan to jack it up and support it on a temporary beam in that corner. Replace the lower plate and put in new 2x6 studs then attempt to gradually pull it back with cables and straps at each corner on two sides, going to and through timbers lagged on the inside and outside of the top plates, over posts that pivot off of the foundation and down to posts. I too plan to use a come-along for applying the force. If I get it straightened I'm thinking of using some heavy OSB screwed onto the inside walls at the corners.