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So I decided to get the Kwik Sew 3338 that I've used before to make a plain long-sleeved t-shirt (I have decided that plain t-shirts, while practical, don't do much for me). I put the traced off pattern up against the $5 top and finangle it about to get the same shape. The front is one piece from the neck down and two side bits that go up to the shoulder seams.
Great explanation, isn't it?
Here's the result - I am rather pleased. One more tripfit done!
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Note it didn't cost $5 - I used leftovers from something else and a pattern I already had.