83 550 ltd -> gpz front wheel swap

I want to swap the front wheel on my 83 550 ltd (chain driven, dont know if that makes a difference) with one from a gpz so i can fit dual discs, and was wondering if it would be a direct swap, which is to say are the axles the same size, and would the rotors line up. I have mounting points for dual rotors on my forks, and was kind of assuming that they are the same forks, or if not, maybe the same dimensions. I've found several sets of brakes on ebay, but want to know what I'm getting into before I get into it.