how wide can i go?

[Maysik]

thats basically what i am after i also had 10'' hotwires on the rear of a wb ute but still had to modify the lip. but i need to know how much backspace i have on the hz van before i start looking at combinations.

Lot of factors to consider when copying someone else's set up. I will find it difficult because I have a non standard diff, it's a disc brake rear from a Statesman that puts the hubs outboard 9mm.

Perhaps you might have to bite the bullet and take the wheel off and measure offsets and centres etc and go to a fitment guide. That way it will be dead accurate for your vehicle. Most wheel websites have them, I know Dragway has a good one.
Hope this helps.