I suggest you draw a new fender pattern to ensure the top and bottom are square. This isn't as critical with the half stirrup leathers that you have, but I like things to be straight. Assuming they are 3 inches wide, you draw a rectangle 3 inches by the length of the old fender. Then you can use the old fender for general shape and use a little artistic freedom to make them look appealing.
Sounds like you are going to twist and wrap the new fenders. If so, I have a couple tips that make it easier (at least for me).
Randy