There isn't anything tricky about this process since you're asking about a Model Seven being re-barreled. I've build dozens of 6.5 GAP 4-S (6.5 SAUM) on these actions. It's just a slightly shorter M700 action. Your action already has the box and follower so it shouldn't be any problem.
I guess that will depend upon which 140 grain bullet you're asking about?
If it's the Berger 140 grain Hybrid, using an OAL of 2.825" there will be 0.393" of the shank length in the neck and 0.617 of the bullet seated into the case.
Using a DBM you can go as long as 2.925" when the spacer is left out.