The quick way? Take the torque tube and center section out of your existing rear axle housing. Put the center section from the 55 in your existing housing. It will bolt right in. Axles will fit too. You should replace all related seals and check the bearings.
Install your open driveshaft tranny, should bolt right in. Get a drive shaft made.
Now the important part. Weld the pivots solid on your existing housing. The torque tube housing pivots at these points because of the lack of u-joints. With an open driveshaft with u-joints, the u-joints provide the pivot and the originals pivots have to be welded solid.
Are you confused yet? I did this to mine and have not had any troubles. If you need me to post pictures of my setup, let me know.
Point is, you do not have to change the housing unless you want to center the wheels in the fender opening. If you want the wheels centered, you will have to make new axle mounts.
