This is a response for Marlo to a post in the Body forum.
I have been working on a '60's Chev pickup rear suspension swap into an AD frame over the last couple of years. ( I work kind of slow.... ).
Here is a link to pictures of my frame. \'49 chassis with \'66 pickup rear suspension
I made drawings of the frame and the '66 suspension in a Computer Aided Drafting program (AutoCad) and then proceded to make the mods to the frame based on the drawings. The only obstacle was that the spring pockets are right at the outside edge of the frame on the '49. I made the cut in the bottom flange right out to the vertical section of the frame and then welded in a curved piece of metal that tied the bottom flange into the 2X4 cross member. The pictures at the link posted above show the installation of the '66 cross member that anchors the trailing arms and the new transverse link.
Give a yell if you've got more questions. My wife got a new digital camera for Christmas so pictures are a lot easier to post than they were when I made these pictures