IMO You basically really need the later trunk floor to do it. Just later straps and brackets won`t cut it since the 76 floor has a completely different shape. You could locate a used trunk floor and drill out the spot welds and replace the whole trunk area. Anything other than that may look...
call Leon at Silke's Auto Parts Inc JACKSONVILLE, FL 32217 they show 2 in stock. 4058129 there is also a superseded part number that I forget at this moment.
They are hard to find new on a 2dr. I never tried to find one for a 4dr. Probably getting obsolete also Ask for the part number so you can do your own search Looks like it may be DW859T. Classic Industires shows them online. Not sure if the really have one
In my 78 book 4057086 is the rear link kit for our 78 volare. Should be the same as yoursI would think. I have only one NOS kit you will need two. The other two bushings at the frame mount are not listed separately from the sway bar itself.