Take the stock car specs with a grain of salt because they were designed for 112 and 115 inch wheelbases. Quite a bit different than your Cudas 108. Weight distribution for you will be key, especially with an elephant sitting on the nose.

No one makes 1.26 or 1.28 T-bars any more. Mopar did make 1.22 bars up until the late '90s early 00s, but they are no longer being made. You can sometimes find them on for sale forums, otherwise you may be limited to a 1.18. However, if you really have everything speced around that, talk to Dick at Firm Feel and see if they could whip up a one off set at 1.24, which, coincidently, is the biggest you can put in the factory E body sockets. To go bigger, you need to convert to C body sockets.

Also, are those rates you have calculated including sway bars at all? You want to look at total roll couple front to rear against total weight, split weight and dynamic weight, which will include sway bars and cross weight in the formula. If you are strictly looking at spring rates and then add s-bars on top of that, your balance is shot. However, since T-bars are a limiting factor, you can often manipulate balance using s-bars and leaf springs.

I'd recommend recalculating with available T-bars to back into a complimentary leaf spring number. There are limited T-bars out there, but you can spec out leaf spring rates pretty easily. Additionally, by setting up a tubular sway bar set up with modular links, you can really dial in the sway bar part of the formula using a variety of diameters and wall thicknesses to get things exactly where you want.