Roll couple is the term that is used to describe the amount of load each end of the car is going to need to handle. Since there is more weight on the front, you want more roll couple % on the front to control it. This is why you would go with higher wheel rates up front. Wheel rates are measured directly at the tire contact patch on the ground and are a combination of the torsion bar and sway bar up front and the leaf spring and sway bar out back.

You are going with the highest over the counter wheel rates possible on the nose of your car. You will need a corresponding increase in the rear to match it. As such, you could go with the stock XHD springs at approx 140# spring rate, (actually less than that at the wheel once motion ratios are applied) they are quite a bit under the 300# wheel rate the t-bars produce (not including the sway bar mulitplication), so you may need a 3/4 to 1 inch rear sway bar to match things up, depending on your personal preference for under/oversteer.

Another option to consider is going to an oval track supplier such as Speedway Motors and buying leafs designed for turning corners. You can buy specific spring rates from 80 to 200 pounds in monoleaf steel, monoleaf fiberglass, or multileaf steel configurations. When buying these types of springs you will need to specify the free arch you want. 4" should be about right as once they are installed and loaded, they will lie flat.

Again, consideration of using a rear sway bar will factor into deciding the springs to get. In general I'd say go softer then add sway bar sizing to dial things in or you could go heavier and not use a bar at all. For a ball park guess, I'd say 160# if using a bar, or 200# with no bar.

For a point of comparison, Mopar's oval track leaf springs are 120# and are completely flat when installed. These are recommended for use with torsion bars up to 1.16 with a 1" sway bar and no rear sway bar. The XHD springs are in the 140# range, SS springs are typically 160#. However, the SS springs also have a fair amount of arch to them which is great for the starting line leverage required for drag racing, but not great for round the corner handling.

Personally, I don't think a 1.22 is that radical for a performance handling application. By comparison, the 300# wheel rate these produce would be along the lines of a 600# coil spring in a GM. There are a lot of Camaros out there running 600# springs in the G-machine genre. When I was running oval track, we routinly used 800 and 1000 pound springs up front with 160 to 200 pounders out back. I also liked the car plenty loose and this got it there.