Look at the picture here;

http://www.google.com/imgres?imgurl=h ... =2&ved=0CDsQ9QEwAw&dur=52

What you will notice is a somewhat common 4-link type of set up. In the photo the converging links are on the top of the diff housing and the diverging are to the bottom. I would suggest reversing this for a couple of reasons. 1) if you do the converging links on the bottom you can use the forward mounting point of the leaf springs to attach the lower trailing arms. This will save some fabrication. 2) this sets the roll center at the bottom of the diff housing.

You can the fabricate the upper links by making an attachment that can be held in location by the u-bolts and plates but leaving the leaf springs out of the system. Take the forward point of the trailing arm attachment to the cross-car "beam" under the seat. Fabricate some attachment points and weld them into the car there. As this is for road use (I presume) use 3/4 inch rod ends. (On a car the size and weight of the 1200 this should be more than enough, they use this sizing on 700+ HP pavement late model stock cars)