My friend was up here visiting for the weekend, and we spent a good chunk of time being sewing geeks. I was able to make a permanent kirtle pattern for myself, and for her. We also made a quick dress for my friend. She had several yards of a blue/green/white plaid fabric which we made into a gown for her. The plaid pattern in the bodice will line up if it is ladder laced or fastened with hook and eyes or frogs. (The spiral basting kept pulling the gown up on her right side).
We were even able to document the pattern of the gown. This picture is from The Romance of Guiron le Courtois, A tournament. Evidently a plaid non-bias cotte IS period in 1370-80 Italy. Whether it was ever used one hundred years later in Ireland is debatable though. You can find the women wearing a blue and red plaid in the top left. The enlarged image is below. The neckline and the fit of the gown are definitely more pre -Tudor like than the ones in the images, although I did notice that a few of the gowns shown had very square necklines, including the plaid gown.
The following websites has many many images from The Romance of Guiron le Courtois among other manuscripts from the 11th thur the 15th centuries. Click on any picture to see a larger image.