I did that swap in my 59. The width is correct with a standard offset wheel. As for the installation, it's a little lengthy but basically... SUPER IMPORTANT:
center punch your axle centerline on the top frame rail.
Get the k-member centerline and move it forward 1 1/4"! If you don't it'll look like the wheel isn't centered in the wheelwell.
Brace your frame rails up before you cut the cross member out.
Line up axle centerlines. Get your k-member under the frame where it's going to go and scribe the frame with calipers following the contours of the k-member. If you want it down low notch the frame right up to the top frame rail... that's what I did (pictured). After it's in measure everything 1000 times before you weld it up. Box the frame, put gussets to the upper a arm towers, spend the time detailing the edges of the installation and it'll look like a factory unit. I'm going to do another one of those soon
Can't get enough! You can email me at firstname.lastname@example.org for other questions if you want, I have some pictures of the various stages of the install. I don't use this message board much.