As someone between an R and an L in most OTR cuts, I've had a half dozen or so jackets shortened. Here are two things I've come to learn:
1. People telling you to pin it first to see how it looks are 100% correct. My jackets with higher pockets and buttoning points look great and no one would have any clue they were shortened. My jackets with lower pockets/buttoning points look off.
2. When talking a half inch or so, I never shorten the jacket. It's not enough of a difference to take the chance on how it will look finished.
Just passing this experience along. From your pictures, your patch pockets and buttoning point are pretty low, so would exercise caution in messing with your jacket, especially with those beautiful quarters.