Capri front ends has some built in problems, one is the angle the ARB has to level. It runs down to the LCA and since it is also the only member keeping the wheel from moving backwards, this sets up the nose dive under braking. It also does not help that the ARB is thin and very curvy, so wheel control is poor. Much thicker (28-30mm) or double ARB helps to control the wheel, also try and space the ARB mounting points to improve the angle to the LCA. If your category rules allow it, you can add a compression strut from the LCA to the bodywork behind. Or similar to the front, it just gets very busy. Make sure this new member does not fight and interfere with the ARB. In any event, try and limit movement where the ARB attaches to the LCA especially movement to the back) with the washer's shape and nut. You must however leave sufficient freedom for LCA up and down motion and the resultant ARB rotation in the joint.
Front springs needs to still be quite stiff to counteract dive and bodyroll, but use just enough, otherwise understeer and turn-in will remain a problem. Somewhere around 600-650lb, depending on how much your car weighs at the front axle. That would be a std diameter spring with about 14-15mm wire and 3-4 active coils. The extra shocks will help (it was done like that back in the day), but it is also possible to modify or replace the std unit with one to match your spring and also the mass of hub and wheel.
Add camber and castor, almost as much as you can get. Stock Capri does not have much. Depending again on spring rates, wheel and tyre used, camber of between 3 and 4.5 deg, castor 6-7 deg. Generally set to 1-2mm toe in, depending on tyre etc.
At the back the leave springs and solid axle is a challenge. Those small angled tramp bars on top do work, probably better than the ones you have under the spring. They do have short comings and also a problem is they do not work together fully with the leave spring through its travel arc. They need to get longer AND shorter, therefor they are OEM installed with the soft and squishy bushes that likes to tear and break up. For racing you can install a much stiffer and solid bush, but make them length adjustable so you can install them in a unladen position with the axle at std rife height. From there you can try small adjustments to see if it helps one way or the other.
Panhard rod can help (the simple one that runs the width, attaching to body and one end and diff at the other), but again on larger suspension travel it will try and push/pull the diff sideways, fighting with the blades. Adjustable or just carefully made to suit the normal diff position.
Your LS diff will help and allow you to go stiffer on the back. Deradiused leaves and add 1 to 2 blades. One full length main blade just with the eyes cut off and another 2/3 length. Use Capri or any other that fits, same width and thickness. Try and keep the blade rubbing surfaces lubed, it does help. Dont go too hard with the rear shocks, about a std adjustable shock set to Sport/Firm. No ARB's at the back.
Don't go as hard and stiff as you can, just go hard enough to control dive and body roll. After that and in general, stiffer at the front means less turn-in and more understeer through apex. Stiffer at the back means sharper turn-in and more oversteer through apex and exit.