Also need slug size
Besides the measurements you'll also need the slug type and size for the mast. You could take a few measurements of your existing slugs or the track and buy a/some onesies (sp?) at West Marine to check for fit.
If the boom uses a bolt rope you'll need the size for that too. Might be able to go loose footed if need be.
Other little detail may be any mast bend considerations, boom to mast angle, and roach. Too much roach and the leach can hang up on the back stay, especially if it is a full batten main.
Make sure the "new" sail isn't blown out.