Ok, finally over the jetlag (it seems to take longer the older I get) and back into sewing.
I decided to make a muslin of this jacket in some quite heavy green cotton (an Ikea curtain in it's previous life - I like sewing these heavy fabrics, it makes my stash look much smaller!);
Although it's a bit more of a boxy shape than I normally wear I really liked the sleeve and back design. It was easy to put together, the only problem I had was that the jacket had no neck facing pieces or lining and I really thought I had done something wrong. Thanks to help from Marji, Melissa and Tany, I discovered it wasn't me going crazy. Thank you ladies! Tany kindly read the instructions and apparently the jacket is supposed to be lined, and has no neck facing. It's not at all obvious from the fabric layout and I have learnt not to get too hung up about trying to do these patterns exactly as specified in future, but to just do my own thing.
The muslin was looking quite good, and there were no fit issues so I decided to finish the insides so that I could potentially wear this jacket. I still have to decide whether to just do a neck facing or lining or both and sew on the cover button and then it's done. Here is the jacket so far...