Yes, your IC is out way too far for the HP that the car is making at this time. Also, the spread at the rear of the 4-link bars is too close. One way to think about this, is try to lift a sledgehammer out horizontal with your elbows together vs with your elbows apart. When your elbows are farther apart, you can put more leverage on the handle to raise the head. Now lengthen where your grip is at on the handle and shorten where your grip is at. When you get closer to the head of the sledgehammer, you can lift it easier. This is similar forces that the rear end is trying to transmit through the IC.
The CG of the car is at 63" forward (as you balanced) and is roughly located at about the height of the camshaft. If you plot from this point to the bottom of your rear slicks this is your squat/anti-squat line. If when you plot out your IC from the rear end and it falls below this line, the car body will try to squat down over the rear tires. If the IC falls on this line, then the car will not try to squat or raise in the rear. If the IC is above this line, then the car will raise up in the rear. I have my car set up to squat a little in the rear, so the IC is below the squat/anti-squat line.
I use this for an initial start, but I really adjust to what the car wants. Every car is different, so you will have to adjust on the bars and the shock settings, and even possibly the springs. The rear springs only need to be stout enough to hold your car up to the correct height on your shocks. My shocks are supposed to be set to a compressed ride height of about 14.5". So you adjust the spanners on the coil springs to get to this height and then you adjust the shock mounts to get the ride height on the car. This allows for the shock to be close to the middle of its range to allow for compression and rebound.
JMO
Bill Mitchell