Swop a Sea&Sea MDX Pro Mark III housing?

I have a Sea&Sea MDX PRO Mark III for a Canon 1Ds Mark III. I want to swop it for a Sea&Sea MDX PRO 5D Mark II housing. I've used both the 1Ds Mark III and the 1D Mark IV in the housing. I'm wanting to shoot more video and the housing needs to be modified to shoot video o the Mark IV. I also need a smaller housing for the type of work and the amount of travel I'm doing.