Mike,
When I purchased my GT the first thing I could not stand was the high rider stance and the excessive roll in the corners so I installed a set of lowering springs with the expectation that the lower ride height would lower the center of gravity and improve the handling, wrong! It still handled like crap, too much roll in the corners so I bought the koni's. However, I realized that the missing rear bar is really effecting the handling of the GT, not so much the shocks as they are not going to control roll like the bars will. Since I had already installed the springs it was a lot easier to install the bars and see how the GT handled after installation and like I posted before, it was a completely different animal! Very happy with the handling at this point. The koni's will only make it better!
The shocks dampen the spring oscillations so if your cruiser did not have a bouncy rear end before the spring install there is no reason it should be after the lowering springs were installed and this is what I don't understand.
There is no such thing as preloading the shocks. If they are adjustable then you can set the dampening but you can not "preload" a shock, it is not a spring. The only problem with the stock shock is that the travel is reduced and they may bottom out sooner than an aftermarket shock designed for a lower suspension. In no way am I saying that the stock shocks are the best set up, far from it, only that they should work fine until money can be saved for a good set of adjustable shocks, such as the koni's which are expensive.
In a nut shell; what I am saying is that I would install the sway bars ,even before lowering springs, if you want this PT cruiser to even remotely handle in the corners and I would also recommend the larger after market bars rather than just adding the stock rear bar.
Just my 2 cents.
