When I talked to the ARB guys they said you can stack them but not more than 5mm if you already have a t0mm, but you can take that with a grain of salt. He also said that when you do the ARB lift nobody puts it in and gets it done the first time. He said sometimes you have to play with the spacers and even may have to swap the AB springs from side to side depending if it leans or not.I think it's gonna be trial and error to see what looks right. My guess is stack them and yank the rear. Dirk also mentioned never measure hahahaha it messes with your head. Just go by what you see and like. I laughed
I don't have the answer for you because I started this thread with the same exact questions. I am waiting for my new springs and figure I will be putting them in and taking them out and trying different things. I have some 3/4's on the side in case I need them. I will keep you posted, but I can see that this was a good question. I was feeling kind of alone with this issue, but I see now that others are struggling the same as me.
Good luck and keep us posted on your progress as I will too.