Too much work, but 73-87 1/2 ton rear will work. It will be 1.5" wider, but that's a plus....it fills the wheelwells better, even if you have wider wheels.
the ujoint & driveshaft will fit the new rear.
-cut off pads from BOTH rears and put the 69s on the donor.
-fabricate a new panhard bracket to weld onto the donor rear; or cut one off of a 60-63 pickup rear.
-now the panhard bar will be too short, so you need to lengthen it.
The bar deal is due to the fact that 64-72 rears have a boss casted onto the top of the center housing, so the threaded stud can fit in it. That's where the panhard bar hooks to. You can't duplicate it, so you need to build your own bracket (which you will not be able to get in the correct spot to use the stock bar)
It's too bad you don't have a 70, because that one year rear end can use the later 5 lug axleshafts & drums.......69 is too narrow