When double disking the 77 and up front end there is the option of using SR500 left side components. SR500 disks are 5mm thick instead of the XS 7mm. SR500 front brake parts are a simple bolt on mod.
If 5mm thick discs are used on both sides, the added weight of double disking is reduced. And, its relatively easy to find SR500 parts.
I've done this and do intend to do it again as well.