Duster Frame Repair

Hey guys, I'm restoring a 73 Duster and I have to repair the rear frame rails. I had to cut the left side and have had a new piece made. What I'm looking for advice on is the best way to put it all together. Should I "butt" the new piece up to the frame, or "sleeve" it over the existing and weld it up. Any pointers or advice would be greatly appreicated.

Thanks in advance,

Matt

PS. Pics of my project are in the members restoration section.