Well, last years Rochester festival was off the menu for us due to the snow, so it never really got made... till this year!
I did indeed use pattern 1 from the above post as my main resource, sizing up the front and back pieces according to John's chest measurement. I resized the sleeve pieces with the same scale, but ended up removing quite a lot of the back of the sleeve at the muslin stage.
Another change I made and later regretted was changing the dart at the top of the sleeve to be more of a gradual curve, once I'd got the whole thing assembled and on John (rather than on my female dummy), I realised that a slight squaring of the shoulders as indicated by the pattern would probably have looked better.
I used a shower curtain to line the sleeves and the top section of the back. I was determined that this time John wouldn't be getting cold and wet while I was wrapped up warm!
Here is the muslin: