Before cutting, I sewed the new seams and tried it on to check the fit.
The hardest part was sewing on the sleeves. I had made the shoulders 1 1/2 inches narrower on both sides, and the body of the shirt about 2 inches narrower. The arm holes are curved. I made multiple tries before getting it right. All in all, I'm pretty happy with the shirt and now I can wear a walk down memory lane. I'm also pretty happy with the seams. The original shirt had flat felled seams, which dont have any rough edges insidecor out. I could have zig zagged the new seams, but they wouldn't look as smooth or as nice. Flat felled edges are not too hard, and my result was OK for a novice.