The below modifications aren't complicated, they just require some quality time with a pencil and a ruler.
A quick overview of the changes:
- Optional - Lengthen the sleeve by 5cm
- Optional - Lengthen the body by 10cm
- Optional - Add a 1.5cm centre back seam
- Lengthen the centre front line to draw in a new round neck line
- Make new facings
- Optional - Mark the position for back split
- Mark button placement
First of all I lengthened the body and arm as per the above measurements using the lengthen/shorten lines included on the pattern. Re-draw the side seam and sleeve seam line from underarm to hem after lengthening. This is completely personal preference as I wanted a longer length and a back split, but you can skip this stage if you just want to get to the round neck bit!
Next mark the 1.5cm seam allowances on the armhole edges of the front, back and sleeve pattern piece as well as adding a 1.5cm allowance to the centre back ready for creating a back split.
If using a neckline from an existing pattern then mark the seam allowances of the shoulder and neckline. For the fronts match the centre fronts of both patterns and and either raise up or down until the shoulder/neck point meets the shoulder dart line of the coat. Do the same with the back and draw in your new neckline.
Extend the centre front/grainline up to the new neckline so it is there as a reference point for your button placement.
Whilst all your pattern pieces are taped together in this way re-draw a new facing for the front and neck edge. Use the existing facing pieces as a guide for the width of the new facings and blend them together between the neckline and the front edge. Mark the position of the armhole seams and shoulder dart so that you can make notches to aid your sewing. This will be a one piece facing with a centre back seam.
Mark the position of your centre back split. Mine was about 25cm from the bottom edge. I left the seam straight, but folded the seam allowance back at an angle from the end of the back seam to the bottom edge so that the split edges don't meet.
Other than that I marked the new button placements about 13cm apart I think and sewed the buttonholes according to the size of the buttons. The outside edge of the buttonhole is in line with the centre front of the coat and the buttonhole extends towards the armhole from there (if that makes sense).
As touched upon in my previous post, I bound the centre back seams open, but the rest of the seams were bound together. The seams may look a bit like maze when it comes to the binding, but I started by doing the sleeve seams up to the gusset, the front armhole down to the underarm and then the back armhole down to the hem.
The top of the welt was topstitched down from the front to keep it against the coat front. This is instead of hand stitching and more appropriate for an unlined coat. Don't look too closely at my embarrassingly poor stitching!!!
The bottom hem allowance was kept as per the instructions and simply topstitched down and the lengthened sleeves were finished with bias tape on the ends and rolled up a couple of times instead of a traditional hem finish. You would need to make a facing if you wanted to hem the sleeves properly because of the tapered ends.
Is this enough info? If you want to have a go at this, but get stuck then give me a shout and I'll try to help!