Sewing tutorial - Man style large shirt to feminine top Part 2

I went ahead and cut the collar and the button bands off, finished the raw edges with an overhang stitch (except for the neckline), then sewed down the front of the shirt with a generous (1 inch) seam allowance.

Here I literally hit the first snag. The neckline in the front is now tiny and no longer matches the one in the back. It's looking like I have to deconstruct the top of the shirt completely and rebuild it. I also need to think about how deep I want the neck line in the front.

This is how the back of the shirt is built. I seam reaped along the white lines (shoulder seams and where the upper back rectangle met the sleeves.

Next I cut out the desired neckline in the front, with the center front seam allowances lying flat. To cut out the neck line, I used a top with a good V neckline and traced it on the black shirt, adding a seam allowance. I folded the shirt in half and cut, to ensure a symmetrical neckline.

This is what it looked like when laid flat again:

Apparel works in mysterious ways. The next step was to completely remove the upper back panel and join it at the shoulder seams with the front shoulders, centering and trimming the neckline to match.

I turned the shirt inside out and laid it back side facing up. I took the detached upper back piece and laid it on top (right sides facing) so it would match at the shoulder seam. I found that I had to trim the front neck line to match at the shoulders (it wasn't as wide a neck opening as what the back had).

After I cut out the front neckline to match, I pinned the shoulders together and identified how much to trim off each side of the upper back piece. A quick fitting helped me verify that the shirt would fit at the shoulders. 

Then I made a mistake and cut the sides of the back piece straight down from the shoulder seam (following the original edge, essentially taking a rectangular piece out on each side. Unfortunately, that was forgetting about the changed curvature of the sleeve seams and so I ended up having the shorten that back piece more than I had intended to (the initial plan being not to trim anything further off that piece). Now I end up with a seam across the shoulder blades that's above the shoulder blades.

The curved sleeves (white) and upper back piece cut straight on the sides (red). Where they diverge, the back piece must be trimmed.