I would not trade the headers. The install is very time involved and not worth all the labor you would have to pay. You would be better served just buying new HREs for the same amount of money and guaranteeing they are perfect shape. I would suggest swapping the wheels and cash. As you said, pointless to offer the exhaust as yours is modified already. The 21 HRE will look great but remember, tyres for 21 are very pricey in comparison to 20s since it is an odd size.
Our site is not down but is being updated and will be finalized by the end of this month. We would love to have you come by, that way you can see the new facility. We have a lot of new things in the works for the S85 application. They should be done by the time you come to visit us in Feb. Until then have a Happy Holiday and New Years!