I am so glad I tried this. Grading the pattern was fairly easy math, and I ended up developing a method that I really like.
First I slashed the pattern in 3 parts, then held it together with some scotch tape. Then I used very wide masking tape to join the two pieces together, after which I turned the pattern around and lined it with newspaper.
I did a rough cut-and-piece with the graded pattern and only found 2 small issues that I feel should be fairly easy to correct.
First, on the above rough cut, I did not put in the neck facing because I think when I graded, I must have forgotten to grade one tiny portion of the front facing.
Second, the armhole was a little tight when I gave the 5/8″ seam allowance; when I lowered it to 1/4″ seam allowance, the sleeve fit much better. This says to me that I probably need to enlarge the arm hole a little bit more.
Overall, I’m super excited. The jacket fit fairly well and I think it will be really beautiful in the light wool that I have prepared for it.