For the rubber mounted Sportsters you will need some sort of a subframe. You may be able to fit a clamp somewhere on the frame for a lower front mount but when it comes to the rear there's nothing structural you can fit a clamp mount to.
Don't count on DMC for details though. They will sell you a subframe for your Sportster for somewhere in the order of $700 but won't provide a photo of it - I asked because I can't afford their subframe but they're worried that the Chinese will copy it. Fair enough, I guess.
So I'll have to make my own. If anyone has done one and is willing to share their design I'd love to see it.
My rear suspension is a Progressive Suspension. My seat is custom made - I stripped the stock seat down to the pan and started from scratch.