As part of a donation drive on LiveJournal, I was commissioned to make two different custom corset patterns. One person specifically wanted an adaptation of the Khaki Corded Corset on pages 62-65 of Jill Salen's book, Corsets: Historical Patterns and Techniques, ISBN-13:978-0-89676-261-9.
Normally, adapting a pattern to measurements is all a matter of mathematics. You proportion out the various measurements within the pattern and adjust them equally to match the measurements of the individual being fitted. In this case, the historic corset was so vastly different in body shape that purely following the mathematics would have resulted in a corset that looked absolutely nothing like the original. As it is, it will have a very different look, but by altering the formation of the pattern to suit the customer's body shape it can look as near as possible.
The main crux of the problem is the wiastline placement and other vertical measurements.
The original corset: 14" busk, 5" to bust top, 2" from underbust to waist, 8" from waist to busk bottom
Adapted pattern: 12" busk, 3" to bust top, 5" from underbust to waist, 5" from waist to busk bottom
To compound the problem, despite being a relatively small corset, the original wearer had a proportionally larger cup size. This last detail is only an issue because the what gives the corset its distinctive look are the gores. A proportionally smaller cup size means that if I stay true to the proportions of the pattern while creating the correct cup size, the gores will look much smaller than on the original corset.
A larger space between the bottoms of the bust gores and the top of the front hip gore is unavoidable. That is a virtue of the customer's body shape, and at my skill level I cannot alter that without creating an ill-fitting pattern.
If you have Jill Salen's book (it is worth having if you are interested in drafting your own corset patterns), open it to page 64 and compare the shapes. I tried to retain the major lines of the pattern, while adjusting it to the vertical measurements of the customer. The more exaggerated angle at the side seam of the front panel is a result of the longer torso. I used the waist and underbust measurements to set the angle, and followed it up to the bust so it would retain the same lines as the original corset. It may need to be curved upward slightly, but that is best determined at the mock-up fitting.
On the scale version I also contemplated artificially dropping the underbust, but changed my mind on the final. The way the gores are shaped, they are intended to cup outwards immediately, so if I dropped them by an inch the customer might have needed to pad the bust in order to fit properly.