Plan A- I don't really understand your obsession to make your wheel choice difficult AND expensive.
I thought you were stuck on a 20" rally style wheel, so I could see the need for a custom wheel. While it's not my preference, I understand what you set out to accomplish.
By the looks of the drawing, you have ventured off that path. I'm not really sure why you would custom build a wheel that IMO looks nothing like what you originally wanted.
Plan B- I think you have absolutely lost it if you spend the time, money and effort to do the 6 lug conversion.
There are several wheels available that look very similar to the pics you posted of the factory wheel. They can be had in 5 lug, in various widths, and backspaces.
Look at some of the high end custom wheels such as Fesler, Fiske, Schott...
