Can't help you with the front suspsension although there are folks on here that have done the front. I'm in the middle of installing the Mark VIII IRS in my 53 right now, should be finished tomorrow. I used the bracket kit from truckIRS.com and it's amazingly easy if you can measure accurately. Dave Held from their site has been extremely helpful in answering my questions before I purchased the brackets and any that have come up since then.

If you look for posts over the past couple weeks in this forum there's a thread on the MarkVIII swap with info from a couple other people that have done it as well, a couple people have done it with the same brackets I'm using and others have completely fabbed the install themselves.

The one thing I'm trying to figure out now is gas tank location. I want to do something that's not in the cab or under the driver's seat outside the frame rail (like the 53 is stock), and the typical mustang tank folks use I don't think will fit in the rear rails of my truck with the Mark VIII IRS installed since the mounting crossmember of the IRS sits so far behind the rear axle. I'm hoping to figure out some other gas tank install that'll fit between the frame rails, but depending on whether you're planning to relocate your 56 in cab tank you may want to consider that before putting the IRS in your truck.

Ralph